METALLURGICAL  PRACTICE 


SOUTH  DAKOTA  SCHOOL  OF  MINES. 


Department  of  Metallurgy. 


Rapid  City,  South  Dakota. 
JUNE,  1904. 


ERRATA 

5%. 

1.  Page  23,  foot  note,  third  line:  Read  bromine  for  brome. 

2.  Page  28,  line  30:  Read  zinc  bromide  for  zinc  bromo. 

3.  Page  28,  line  32:  Read  bromo  for  bromide. 

4.  Page  28,  foot  note:  Read  Simpson  for  Sampson. 

5.  Page  29,  line  12:  Insert  bromo  before  the  word  cyanogen. 

6.  Table  III,  test  No  5,  column  Time  of  Treatment:  Read  k‘and  48 
hours  standing”  for  “48  days  standing.” 

7.  Table  I,  test  No.  4,  column  Time  of  Treatment:  Read  “41  hours  agi- 
tation and  31  days  standing”  for  “60  hours  agitation.” 

8.  Table  I,  test  8.  column  Time  of  Treatment:  Read  “22^  hours  agi- 
tation for  “same.” 

9.  Page  35,  first  table,  Ore  C,  column  “Increase  in  Extraction,”  last 
line:  Read  6 per  cent  for  g per  cent. 

10.  Page  35,  second  table,  in  second  column  heading:  Read  “31  days 
contact”  for  “3  days  contact.” 

11.  Page  52  Table,  Dakota  Mill:  Transfer  figure  “86  tons”  in  column 
“amount  of  solution  passing  while  filling”  to  column  “amount  of  battery 
solution.” 


Oak  Street 
JNCLASSIFIED 


BULLETIN  NO.  7. 

OF  THE 


SOUTH  DAKOTA  SCHOOL  OF  MINES 


Department  of  Metallurgy. 


l. 


, 


2. 


3. 


Sulphide  Smelting  at  the  National  Smelter  of  the  Horseshoe 
Mining  Company,  Rapid  City,  South  Dakota. 

By  Charles  H.  Fulton  and  Theodor  Knutzen. 

Laboratory  Experiments  on  the  Unoxidized  Siliceous  Ores 
of  the  Black  Hills. 

By  Charles  H.  Fulton. 

The  Crushing  in  Cyanide  Solution  Process  as  carried  on  in 
the  Black  Hills  of  South  Dakota. 

By  Charles  H.  Fulton. 


Rapid  City,  South  Dakota 

JUNE,  1904 


THE  RAPID  CITY  DAILY  JOURNAL  PRINT- 


Letter  of  Transmittal. 

South  Dakota  School  cf  Mines,  | 

Rapid  City,  June  5,  1904.  j 

Sir: — I have  the  honor  to  transmit  herewith  a series  of 
papers,  by  Charles  H.  Fulton  and  Theodor  Knutzen,  on  Met- 
allurgical Processes  in  South  Dakota. 

I submit  them  with  the  recommendation  that  they  be  pub- 
lished as  Bulletin  No.  7 of  the  School  of  Mines. 

Respectfully, 

Robert  L.  Slagle,  President, 

Hon.  Ivan  W.  Goodner, 

President,  Regents  of  Education. 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 

University  of  Illinois  Urbana-Champaign  Alternates 


https://archive.org/details/metallurgicalpraOOfult 


Introduction. 

The  successful  treatment  of  the  unoxidized  siliceous  ores  of 
the  Black  Hills  is  a subject  of  vital  interest  to  the  mining  frater- 
nity of  the  region  and  the  experiments  on  these  ores  were  taken 
up  by  the  Metallurgical  department  of  the  School  of  Mines  with 
the  idea  of  rendering  what  assistance  it  could  in  this  direction  to 
the  millmen,  knowing  that  very  often  their  time  and  opportunity 
for  this  kind  of  work  is  limited. 

The  crushing  in  cyanide  solution  process  has  within  the  last 
two  years  assumed  great  importance  in  the  Black  Hills,  and  for 
that  reason  a detailed  description  of  the  process  should  prove  of 
interest. 

The  writer  wishes  to  express  his  obligation  and  thanks  to  all 
those  who  have  so  kindly  and  freely  furnished  him  with  informa- 
tion; his  especial  thanks  being  due  to  Mr.  John  Ingersol,  Mr. 
J.  V.  N.  Dorr,  Mr.  Freeman  Steele,  Mr.  G.  Howell  Clevenger, 
Mr.  John  Cross,  Mr.  Baldwin,  Mr.  James  Hartgering  and  Mr. 
John  Millikin. 

He  wishes  also  to  acknowledge  the  indebtedness  due  to  Mr. 
William  Bowman,  his  assistant,  for  the  faithful  and  careful  work 
done  in  the  experimental  tests  on  the  unoxidized  ores  of  the 
Black  Hills,  also  to  acknowledge  his  indebtedness  to  Mr.  S.  S. 
Arentz  for  much  aid  in  the  same  work. 


Lundborg,  Dorr  & Wilson  Cyanide  Mill,  near  Terry,  South  Dakota. 


Sulphide-Smelting  at  the  National  Smelter  of  the 
Horseshoe  Mining  Co-,  Rapid  City,  S-  D.* * 

BY  CHARLES  H.  FULTON  ANDTHEODOR  KNUTZEN. 

The  plant  of  the  National  Smelting  Company,  a corporation 
controlled  by  the  Horseshoe  Mining  Company,  was  built  during 
1901  to  smelt  the  dry  siliceous  ores  of  the  northern  Black  Hills, 
extracting  the  gold  and  silver  values  in  a matte  of  low  copper- 
percentage  which  is  shipped  to  Omaha  and  Denver  for  refining. 
Originally,  the  plant  was  designed  to  collect  the  values  of  the 
siliceous  ores  is  an  iron-matte,  which  was  to  be  resmelted  with 
lead-ores,  in  a lead  furnace,  the  lead-bullion  produced  to  be  re- 
fined into  Dore  bullion  in  English  cupelling-furnaces,  How- 
ever, the  scarcity  of  lead-silver  ores  in  the  Black  Hills,  owing  to 
the  present  non-productiveness  of  the  Galena  district,  led  to  the 
abandonment  of  this  plan;  and  both  shaft-furnaces  of  the  plant 
were  run  as  matting-furnaces,  the  mattes  produced  being  shipped 
as  above  stated. 

It  is  not  our  intention  to  present  anything  very  new,  but 
rather  to  supplement  the  interesting  and  valuable  paper,  Pyritic 
Smelting  in  the  Black  Hills,  by  Dr.  Franklin  R.  Carpenter.  1 

Smelting  in  the  Black  Hdls  is  a difficult  matter  from  a com- 
merical  point  of  view,  owing  to  the  fact  that  the  only  produc- 
tive material  going  into  the  furnace,  generally,  is  the  siliceous 
ore  and  a little  copper-ore,  the  pvrite,  or  pyrrhotite,  and  the 
limestone,  being  barren  of  values,  and  no  lime-ores,  or  gold  or 
silver-bearing  pyrite  being  at  present  available  in  the  Black  Hills. 
The  recent  price  of  coke  from  the  east  or  from  Colorado  has 
also  been  prohibitive  C$9.50  per  ton),  and  Cambria,  Wyoming, 
coke  ($4.50  per  ton)  is  of  such  inferior  quality  that  it  cannot  be 
used  alone,  but  has  to  be  mixed  in  the  proportion  of  2 to  1 with 

x Trans. , xxx.,  764. 

* [Reprinted  from  the  Transactions  cf  American  Institute  of  Mining  E~ gineers  February,  1904.] 


8 


eastern  or  Colorado  coke,  to  be  able  to  smelt  with  it  nt  all. 

The  National  Smelting  Plant  is  situated  at  the  eastern  end 
of  Rapid  City,  on  a terrace  site  on  a spur  of  the  Fremont,  Elk- 
horn  & Missouri  Valley  Railroad,  a branch  of  the  Chicago  & 
Northwestern  Railway  system.  Directly  below  the  railroad- 
trestle  are  nine  125-ton  bins:  Three  for  siliceous  ore,  2 for  lime- 
stone, 2 for  coke,  and  1 for  coal.  The  bottom  of  the  bin  slopes 
50°  , the  planking  being  protected  from  wear  by  railroad-  iron, 
placed  transversely  every  foot. 

The  material  is  shipped  to  the  smelter  in  20-ton  ore- cars, 
usually  having  a bottom-discharge.  It  is  sampled  by  shoveling 
on  a sampling-floor  at  the  top  of  the  bins.  Lots  of  60  tons  or 
less  are  sampled  by  taking  every  fifteenth  shovel,  while  those  in 
excess  of  60  tons  are  sampled  by  taking  every  twentieth  shovel. 
The  sample  is  thrown  down  a shute  at  the  side  of  each  bin, 
carried  by  a barrow  to  the  sampling- works,  and  is  there  crushed 
in  a 9-by  15-in.  Blake  crusher  which  divides  it  into  halves  by  an 
‘‘A”  discharge,  one-half  going  directly  to  a pair  of  24-  by  12-in. 
Allis-Chalmers  rolls.  The  discharge  from  these  rolls  is  re- 
shoveled,  every  fifth  shovel  being  taken  as  the  sample,  or  every 
tenth  shovel,  if  the  ore  lot  is  more  than  60  tons.  The  sample  ob- 
tained in  this  way  is  crushed  in  a pair  of  12-  by  12-in.  sample- 
rolls,  then  coned  and  quarted  on  a plate-floor,  and  the  resultant 
sample  ground  in  a sample-grinder.  The  moisture  is  determined 
at  once  on  the  sample-floor,  in  a specially  provided  drying-cup- 
board. 

FURNA  CES — There  are  two  blast  furnaces,  one,  a copper- 
matting furnace,  144  by  38  in.  in  cross  section  at  the  tuyeres,  and 
15  ft.  in  height  to  the  downtake,  and  the  other,  a lead-furnace, 
120  by  36  in.  in  cross-section  at  the  tuyeres,  and  of  the  same 
height  as  the  copper-matting  furnace  The  lead-furnace  is  used 
as  a matting-furnace  by  bricking  up  the  well.  Both  furnaces 
have  removable  hearths  placed  on  trucks,  and  the  off-take  at 
one  end  just  below  the  feed-floor.  They  are  charged  by  a 
specially  designed  bottom-dump  charge-car,  running  directly 
over  the  furnace-top,  In  our  opinion  this  method  of  charging  is 
the  most  desirable  one.  No  trouble  from  fumes  is  experienced 
on  the  charge-floor.  The  furnaces,  however,  could  easily  be  in- 
creased 4 ft.  in  height,  which  would  enable  better  work  to  be 
done  in  them. 

Steam  is  furnished  by  two  200-h.  p.  Stirling  water-tube 


9 


* * boilers, .-with  a steam -pressure  of  125  lb.  per  square  yich.  A No. 
8 Green  blower  furnishes  blast  for  tiie  large  furnace,  and  a No. 
7 blower  of  the  same. type  for  the  small  furnace.  Both  blowers 
are  directly  connected  to  horizontal  engines  on  the  same  bed- 
plate. The  blowers  run  from  130  to  150  rev.  per  min.,  furnish- 
ing blast  at  a pressure  of  from  14  to  18  oz.  per  square  inch.  The 
blast  main  from  the  large  blower  is  30  in.  in  diameter,  and  that 
from  the  small  one  24  inches. 

The  coal  is  of  a very  poor  grade,  being  slack  from  Cambria, 
Wyo.,  which  costs  $2.75  per  ton,  delivered  at  the  plant.  The 
ashes  are  sluiced  from  the  boiler-plant  through  lauders  to  the 
slag-dump.  The  water-supply  of  the  plant  is  obtained  by  pump- 
ing from  Rapid  Creek,  a few  hundred  feet  below  the  plant. 

SLAGS — Table  I,  gives  the  analyses  of  typical  slags  made 
at  the  plant. 


Table  I— Analyses  of  Slags. 


1 

Kind. 

Silica. 

Ferrous 

(xid». 

Lime. 

I 

Alumina 

Zinc 

Oxide. 

Blowing  in  sing 

Per  Cent. 

42-65 

47-5 

50.2 

42.86 

Per  Cent. 
16  67 

18.7 

16.35  f 

17.24 

Per  Cent. 
3°-7 

28  25 
28.30 

26.  6t 

Per  Cent, 
6.85 

3-5 

4.2 

9-39 

Per  Cent. 

Typical  slag 

Typical  slag 

High  alumina  ar  d zinc 

2.28 

The  precious  metal-content  of  the  slags  given  in  Table  I 
are  usually,  gold  0.01  oz. , and  silver  0.20  oz.  per  ton,  a trace  of 
copper  also  being  present. 

The  limestone  used  as  a flux  is  very  pure,  as  shown  by  the 
analyses  given  in  Table  II,  and  contains  only  a trace  of  mag- 
nesia. Some  magnesia,  up  to  8 or  10  per  cent  replacing  lime, 
would  be  desirable,  owing  to  its  greater  silica-saturating  power, 
anddhe  lesser^specific  gravity  of  the  resultant  slag.  The  Golden 
Reward  plant  at  Deadwood  uses  a magnesian  limestone  success- 
fully. At  the  present  time- no  limestone  containing  magnesia  is 
available  in  the  vicinity  of  Rapid  City. 

The  slags  are  fluid  and  flow  readily  from  the  furnace  with 
a slight  arch.  They  chill  quickly,  which  indicates  a rather  high 
temperature  of  formation.  Water-cooled  slag-spouts  have  been 
tried  on  the  furnaces,  but  had  to  be  discarded  owing  to  their 
« marked  chilling-effect  on  the  slag.  The  greater  part  of  the  slag 
" is  granulated  by  waste,  water  from  the  furnace-jackets  and  dis- 
charged to  flat-cars,  of  the  railway  which  utilizes  it  as  road- 


i 


IO 


ballast.  The  slag  flows  from  the  settling^pot  in  a thin  stream, 
falling  from  a height  of  4 ft.  and  strikes  the  water  which  flows 
in  a heavy  cast-iron  gutter  of  semi-ellipsoid  section,  8 in.  wi.de 
and  6 in.  deep,  inclined  3 in.  per  foot  for  the  first  10  ft.  The 
section  of  the  gutter  beyond  the  first  10  ft.  is  of  a larger  cross- 
section,  and  inclined  but  1 in.  per  foot.  Owing  to  excessive 
wear,  the  section  of  the  gutter  where  the  slag  strikes  it  has  to 
be  frequently  renewed. 

Heated  blast  is  used  in  smelting.  The  blast  heating  appa- 
ratus is  a U-pipe  stove,  containing  12  U-pipes  each  16  in.  in 
diameter  and  10  ft.  high.  This  type  of  stove  is  not  as  efficient 
as  it  might  be  owing  to  the  difficulty  in  preventing  leakage.  The 
stove  is  placed  in  the  dust-chamber  directly  beneath  the  down- 
take,  it  being  intended  to  heat  the  blast  only  by  the  waste  heat 
from  the  furnaces.  Under  ordinary  conditions  the  temperature 
of  the  blast,  taken  at  the  tuyeres,  is  1 3 1 0 Fahr.,  with  the  outside 
air  at  65°  Fahr.  With  the  cupelling-furnaces.  running  on  some 
experimental  work,  the  temperature  of  the  blast  at  the  tuyeres 
was  as  high  as  320°  Fahr  , with  the  outside  air  at  770  Fahr. 

The  flue  of  the  plant  is  of  the  zig-zag  type,  350  ft.  long,  ex- 
tending up  hill  to  a plate  iron  stack,  10  ft.  in  diameter  at  the 
top,  and  166  ft.  in  height  from  the  bottom  of  the  flue  where  it 
merges  into  the  stack.  The  total  height  from  the  tuyere-level  to 
the  top  of  the  stack  is  275  feet. 


Table  II  —Composition  o f Materials  of  Furnace-Charge. 


Name  of  Material. 

Silica. 

. ! 
5 i 

i 

fl  ■ 

jo 

6 

o i 5 

i 

Carbon 

V 

ZK 

0. 

0 

w 

.< 

£ 

w 

Per 

Per 

Per 

« er  | Her 

Per 

Per 

Per 

per 

j Cent.  1 

Cent. 

Cct. 

Cent  ! Cent. 

Cent. 

Cent. 

Cent 

Cent. 

Monteeuma  pyrite ... 

>0.35  | 

7 63 

3<-7^  ! 2 57 

0.30 

32-3 

6.50 

Bion  pyrite  

2 7.0^  ‘ 

3 1 . 7.5  I 

37  °3 

Penobscot  ore  . 

Hen  Hur  ore 

61.44 1 
62.56 

7 3.11 

29  2 (a) 
10.7  (a) 
12.36 

0.68  (a> 

trace 

3.01 

Ben  Hut  ore 

7"  1 3 (b) 

*T  * O *t 

. . . 7.2 

Limestone 

/O*  A A 

1.94 

31.62 

5,.6, 

o.63 

Montana  copper-ore. . , *. 

Ashes: 

2147  

22  85 

24.i6 

Cambrig  coke,  30  per  ce^it 

36.57 

4°- 35 

i4  . 

....  a. 01 

1 2.75 

t race 

Fail  mount  coke  

60.46 

37.-09 

* • 

A-shas,  12.5  per  cent. 

1 

b 

U ■ 

(a)  Includes  feme  oxide.  **  (’>).  Fernc  oXide . 


The  Penobscot  ore  contains  from  0.88  to  o.<)6  oz.  gold  and 
from  1 to  2 oz.  silver  per  ton.  The  Ben  Hur  ore  contains  from 
0.73  to  0.80  oz..  gold  and  1.5  oz.  silver  per  ton.  It  is  generally 
aimed  to  keep  the  ore-value  not  less  than  $20  per  ton. 


- 1 1 

MA  TTE — The  first  matte  produced  is  low  in  copper,  con- 
taining from  io  to  14  per  cent  copper  and  from  4 to  5 ox.  gold 
and  from  6 to  7 oz.  of-silyer  per  ton.  The  matte-fall  figured  on 
the  total  furnace-charge  is  from  4 to  5 per  cent,  this  fall  being 
amply  sufficient  to  collect  the  values.  We  believe  a 3 per  cent 
matte-fall  would  be  sufficient.  It  was  found  by  experience  that 
some  copper  was  absolutely  essential  in  order  to  have  the  matte 
cpllect  all  of  the  values  and  at  the  same  time  to  produce  suffi- 
ciently clean  slags.  In  ipoi,  shortly  after  the  plant  was  started, 
it  was  endeavored  to  run  without  copper-ores,  owing  to  the 
difficulty  of  procuring  them.  Mattes  were  made  with  only  a 
trace  of  copper  in  them,  but  the  slags  invariably  contained  from 
$i.oo  to  $2.50  in  value  per  ton  in  gold.  This  loss  being  too  great 
for  profit,  copper-ores  had  to  be  procured.  Upon  the  addition 
of  copper-ores  to  the  furnace,  the  abnormal  loss  of  value  in  the 
slag  disappeared,  dropping  to  the  normal  value  of  from  20  to 
30  cents  per  ton  and  often  less.  It  has  been  demonstrated  by 
Dr.  R.  Pearce2  and  E.  G.  Spillsbury3  that  iron  sulphide  will  not 
collect  gold  and  silver  Metallic  iron  will  collect  gold,  but  prac- 
tically no  silver,  as  Dr.  F.  R.  Carpenter  has  pointed  out4 — a fact 
which  is  amply  proven  by  the  sows,  or  metallic-iron  accretions, 
formed  in  the  hearth  of  the  furnace  as  well  as  in  the  fore-hearth. 
The  matte  formed  rarely  contains  more  than  30  per  cent  sul- 
phur, while  the  iron  monosulphide  contains  36.36  per  cent,  so 
that  the  matte  is  evidently  a subsulphide.  It  also  contains  me- 
tallic iron,  which  can  readily  be  abstracted  by  the  magnet.  We 
agree  with  Dr.  Carpenter  that  it  is  this  metallic  iron  in  the  matte 
which  collects  the  gold,  but,  unfortunately,  it  is  rarely  in  the 
matte  in  sufficient  quantity  to  give  clean  slag^.  Paradoxical  as 
it  may  seem,  the  quantity  of  metallic  iron  formed  in  the  furnace 
is  due  to  a large  extent  to  the  amount  of  oxidation  which  takes 
place  in  the  furnace.  This  point  is  referred  to  later  in  this  paper 
under  the  section  devoted  to  sows. 

The  amount  of  oxidation  being  difficult  of  control,  thematte- 
composition  and  matte-fall  vary  from  time  to  time.  There  are 
occasions  when  practically  no  matte  is  being  made,  but  the 
Same  time  the  slags  do  not  increase  in  value,  showing  tha  t while 
no  matte  is  made,  metallic  iron  is  being  produced.  This?  condW* 
tion  of  affairs  occurs  during  periods  of  much  oxidation,  and  is 
usually  remedied  by  the  charging  of  extra  quantities  of  pyrite, 


2 J'ntf/s.y,  xviii'. 


4.54 


s Trans.  I xv. , 767. 


4 Ob  cut. 


12  „ 

' . i 'i  . 

in  order  to  furriish  mor.e  sulphur,  and  leave  ;some  to  remain  in 
the  ma'tte.  *- 

Accretions^on  the  furnace-walls  will  decrease  tne  quantity  of 
matte  made,  by  raising  the  zones  of  oxidation.  Of  course,  the 
quantity  and  pressure  of  the  blast,  also,  greatly  influence  the 
matte  producion. 

f DESULPHURIZATION — The  matte-fall  being  generally 
but  4 or  5 per  cent,  shows  the  great  desulphurizing  action  of  the 
furnace,  which  amounts  ordinarily  to  from  70  to  77  per  cent.  To 
take  the  workings  of  a typical  day,  the  quantity  of  sulphur  fed 
into  the  furnace  in  the  shape  of  pvrite  was  7,350  lb.  and  the  sul- 
phur in  the  matte  was  2,100  lb.,  showing  a loss  of  sulphur  of 
5,250  lb.,  which  is  equivalent  to  71.5  per  cent  of  the  total  quan- 
tity in  the  materials  charged  into  the  furnace. 

The  desulphurization-figures  for  December,  1903,  were  as 
follows:—The  quantity  of  sulphur  fed  into  the  furnace  in  pvrite, 
175  tons;  in  matte,  37,5  tons;  in  copper-ore  and  concentrates,  27 
tons,  a total  of  239.  5 tons.  The  sulphur  in  the  matte  produced  was 
52  tons,  showing  a loss  of  sulphur  of  187.5  tons,  or  78  per  cent 
of  the  quantity  charged  into  the  furnace. 

The  sulphur  in  the  materials  carried  over  mechanically  in 
the  flue-dust  may  be  disregarded  on  account  of  its  relatively 
small  quantity  and  the  fact  that  much  of  it  is  in  an  oxidized  con- 
dition. The  total  quantity  of  flue-dust  produced  in  treating  3,- 
952  tons  of  charge  amounted  to  10  per  cent,  or  395.2  tons,  hav- 
ing an  average  sulphur-content  of  3 percent,  which  is  equivalent 
to  1 1.8  tons  of  sulphur,  a large  portion  being  in  an  oxidized 
form. 

The  matte  produced  without  copper-ore  was  made  with  the 
furnace  running  on  pyritous  material  of  the  following  composi- 
tion. Iron,  24. 52;. silica,  27;  lime,  3.06;  lead,  5.82;  zinc,  8.  55 ; 
sulphur,  28.03;  arsenic,  3-4  Per  cent;  copper,  trace;  gold,  0.04 
oz,,  and  silver,  2.86  oz.  per  ton. 


Table  III  .—Composition  of  Mattes. 


Kind. 

Iron. 

Copper. 

Sulphur. 

Zinc. 

Gold. 

Silver. 

Made  without  copper  ore 

Ma’te  made  with  1 ttlc  topper-ore .. 

Mat,te 

Per  Tent 
6i.  r 
68.5 

Per  Cent. 

. 1.6  • 

3.5Ca) 

‘ 5.  s'? 

Per  Cent. 

- 27-9 

Per  Ct. 
2.18 

Ounces 
Per  Ton 

7.1 

4.2 

17-65  - 

17.ll 
IT-73 
II.62  " 

Ounces 
Per  Ton 

9.7 

8.7 
10.25 
2i.4 
I9.7 
i8.76 

Typical  'Matte 7 

* 

. 22.6,  . 

-26.5 

I9-3- 

30.0 

1 ypical  Matte 

Typical  Matte.  . 

f 

(a)  Ttiesla^  acco'mp.mying  this  matte  had  an  ^ssay  vaftie  of  $1,40  perton. 


13 

It  is  worthy  of  note  that  while  some  of  the  zinc  enters  the 
matte,  practically  no  lead  does.  The  analysis  of  the  slag  corre- 
sponding to  this  matte  is  given  in  the  Table  I under  the  name, 
“High  Alumina  and  zinc.”  The  quantity  of  copper  in  this 
matte,  r.  6 per  cent,  is  insufficient  to  give  a clean  slag,  which  in 
this  instance  had  a value  in  gold  of  $1.20  per  ton.  When  opera- 
tions were  first  started  at  the  plant  an  experiment  was  made  of 
adding  lead-ores  in  quantities  equaling  those  of  copper-ores  now 
added,  to  ascertain  whether  lead  would  enter  the  matte  and  re- 
duce the  abnormal  losses  in  the  slag.  However,  no  lead  was 
found  in  the  matte,  for  the  reason  that  the  conditions  under 
which  the  furnace  was  operated  precluded  its  entrance  into  the 
matte.  There  is  so  much  oxidation  that  most  of  the  lead  be- 
comes volatilized  to  the  great  detriment  of  the  yield  of  silver. 
Lead,  even  in  small  quantities,  is  very  undesirable  in  sulphide 
smelting. 

The  first  matte  produced  is  generally  resmelted  twice,  the 
third  matte  being  the  shipping- matte.  The  Table  IV  shows  the 
concentration: 

Table  IV. — Concentration  of  Gold  and  Silver  in  Matte. 


Matte. 

Copper. 

Gold. 

Silver. 

Per  Cent. 

Oz.  Per  Ton. 

Oz.  Per  Ton. 

F rst 

13.5 

4.04 

6.03 

Second 

21.5 

10.05 

15.6 

T!  ird 

22.6 

17. 1 1 

21.4 

The  matte  is  cast  into  slabs  in  cast-iron  molds,  in  order  to 
break  it  up  readily  and  have  it  in  a convenient  form  for  shipping. 

AMOUNT  OF  COPPER  NECESSARY  TO  MAKE 
CLEAN  SLAGS — At  the  present  time,  copper-ore  for  the 
matte  is  brought  from  Montana  at  a considerable  expense,  and  is 
added  in  just  sufficient  quantity  to  produce  the  desired  effect.  It 
is  aimed  to  have  at  least  io  lb  of  copper  in  the  charge  for  every 
ounce  of  gold  present,  and  more,  if  a supply  is  available. 

The  silver  is  much  more  affected  by  the  lack  of  a certain 
proportion  of  copper  than  is  the  gold.  The  ratio  of  silver  to  gold 
in  the  ore  is  from  1.5  to  2,  to  1, and,  with  an  equal  saving  of  both 
metals,  this  ratio  should  be  preserved  in  the  matte.  Mattes 
containing  less  than  20  per  cent  of  copper  show  a distinct  loss 
of  silver.  In  general,  we  do  not  think  that  sulphide-smelting  is 
adapted  to  a close  saving  of  the  silver. 

FUEL — Owing  to  the  high  melting-point  of  the  siliceous 
slags,  the  quantity  of  carbonaceous  fuel  is  considerable.  The 


14 

fuel  expressed  in  percentage  of  total  charge  seems  very  high, 
but  is  explained  by  the  very  poor  quality  of  the  Cambria  coke 
used,  the  ash  amounting  to  about  30  per  cent.  Generally  a 
mixture  of  two-thirds  of  Cambria  coke  and  one-third  of  Eastern 
or  Colorado  coke  is  used.  The  quantity  of  coke  used  varies 
from  14  to  18  per  cent  of  the  ores  and  flux  charged  into  the 
furnace. 


Table  V. — Composition  of  the  Coke  Used  at  the  National  Smelter 


Kind  of  Coke. 

Fixed 

Carbon 

Volatile 

Carbon  Ash,  (a) 

Water. 

West  Virginia 

PerCent. 

85.8q 

65.22 

86  86 

Per  Cent  Pi  r Cent. 

10  12  42 

3-93  29  93 

1 7 lo.7 

Per  Cent. 
0.69 

O.Q2 

1.6 

Cambria,  Wyo 

Colorado 

(a)  The  analysis  of  the  ash  is  given  in  Table  1 1 . 


The  statistics  givea  in  Table  VI  show  a capacity  of  the 
small  furnace  of  about  105  tons  of  burden  per  day.  The  large 
furnace  has  a capacity  of  about  130  tons  of  burden  p«r  day. 
Both  furnaces  operate  under  the  disadvantageous  condition  of 
treating  a very  large  quantity  of  fines,  aside  from  using  such 
very  poor  and  friable  coke. 

COWS — In  our  opinion  the  production  of  sows  is  practically 
inseparable  from  sulphide-smelting  when  high  concentration  is 
done.  The  sows  are  due  to  the  strong  oxidizing  effect  of  the 

Table  VI, — Capacity  of  the  Furnaces  of  the  National  Smalter. 


Material. 

Smaller  Furnace. 
November,  C903. 

Smaller  Furnace- 
December,  1903. 

Ions. 

Pons. 

Siliceous  ore 

1,100 

<380 

Pyrite 

512 

, 548 

Limestone... 

1,058 

1,070 

Copper  ore  etc 

70 

9o 

Flue-dust (a) 

250 

348 

Matte 

136 

125 

Total  burden 

3. 126 

3.j6i 

Coke. 

Cambria 

510 

517 

Eastern 

180 

162 

Fuel  percentage 

18 

17 

(a)  Including  accumulated  flue-dust  from  the  chlorination  works. 


furnace,  as  shown  by  the  following  data.  A desulphurization  of 
80  per  cent;  the  production  of  copper  sulphate,  found  in  layers 
in  the  accretions  of  the  do wntake;  no  evidence  of  carbon  'mon- 


15 

oxide  in  the  furnace  gases;  the  volatilization  of  all  the  lead  fed 
into  the  furnace,  and  the  facts  that  no  iron  goes  into  the  furnace 
as  oxide,  and  the  slag  contains  from  18  to  20  per  cent  of  iron 
oxide  in  the  form  of  silicate.  These  data  make  it  difficult  to 
imagine  that  the  reducing  conditions  in  the  furnace  could  exist 
sufficiently  strong  to  produce  metallic  iron. 

We  believe  that  .the  -sows  are  produced  by  oxidation  in  a 
similar  way  that  metallic  copper  is  produced  during  bessemeriz- 
ing,  taking  as  the  first  stage,  the  melting  of  the  pyrite,  FeS2; 
and  the  loss  of  the  one  atom  of  sulphur  forming  the  monosul- 
phide FeS;  the  second  stage,  the  gradual  oxidation  of  the  sul- 
phur in  the  monosulphide,  producing  a subsulphide;  the  third 
stage,  the  production  of  .some  ferrous  oxide,  part  entering  the 
slag,  and  part  reacting  with  .the  sulphide  present,  producing 
sulphurous  acid  gas  and  metallic  iron,  according  to  the  following 
chemical  equation: 

FeS  + 2FeO  = jFe  SO2. 

Experience  has  shown  that  a larger  quantity  and  higher 
pressure  of  blast  result  in  an  increased  production  of  metallic- 
iron  sow,  and,  from  its  analysis,  it  is  seen  that  it  contains  prac- 
tically no  carbon,  which  apparently  should  be  present  if  the 
metallic  iron  was  due  to  the  reducing  action  of  the  coke. 

In  the  large  furnace  (38  by  144  in.  in  cross-section  at  the 
tuyeres),  a 15-ton  sow  was  produced  in  a 7-months’  run,  having 
an  approximate  value  of  $5,000  in  gold.  In  the  smaller  furnace 
in  a 3-months’  run,  under  a lower  blast-pressure,  a 5-ton  sow 
was  produced,  having  an  approximate  value  of  $1,500. 

The  sow,  as  a whole,  is  not  homogeneous,  and  consists 
mainly  of  metallic  iron  containing  intermixed  slag  and  a little 
matte.  The  metallic  iron  contains  practically  no  silver,  but  con- 
siderable gold.  The  iron  has  a crystalline  structure  similar  to 
that  of  pig-iron,  possesses  a distinct  silver  color  and  is  practically 
pure  metallic  iron.  In  the  large  sow  some  pieces  of  copper  were 
found.  Rarely  a small  button  of  lead  is  found  in  a sow. 

Table  VII.  — Composition  of  Sozv  Produced  at  the  National 

Smelter. 


Material. 

• Iron. 

Sulphur. 

Gold. 

Silver. 

Copper. 

Average  Sow 

Per  C ent 

Per  Cent. 

Oz-  Per 
Ton. 

20.3 

29.6 

35-8 

134-17 

83.8 

Oz.  Per 
Ton. 

2.4 

4.4 
nil 

273.45 

nil 

Per  Cent. 

Crystalline  iron- 

F ore-hearth  sow  (a) , 

99  68 

0,2 

trace 

14.19 

Lead  in  sow 

Copper  in  sow 

(a)  A true  sow. 


1 6 


Material  from  the  fore-hearth  resembling  a sow  contained, 
iron,  72.3;  sulphur,  19.19;  copper,  6.94  per  cent;  gold,  6.3  oz ., 
and  silver,  5.2  oz.  per  ton.  It  is  usually  through  the  accumula- 
tion of  this  material  and  that  of  the  true  sow  that  the  fore-hearth 
is  lost.  The  top  layer  of  the  sow,  as  well  as  that  partin  contact 
with  the  fire  brick,  is  usually  of  an  oxidized  appearance. 

The  treatment  of  the  sows  for  the  recovery  of  the  gold  and 
silver  values  in  them  is  a difficult  problem,  especiallv  when  no 
reverberatory  furnaces  are  available.  The  National  Smelter 
has  not  this  valuable  adjunct  which  is  practically  necessary  for 
the  treatment  of  the  sows  and  the  flue-dust.  At  the  present 
time  the  sows  are  broken  up  by  blasting,  a very  expensive  opera 
tion,  and  re  fed  into  the  furnace  a little  at  a'time  with  the  pyrite 
in  order  to  resulphurize  the  iron.' 

FLUE-DUST — Owing  to  the  absence  of  reverberatory  fur 
naces,  the  flue-dust  made  amounting  in  quantity  to  about  10  per 
cent  of  the  charge  is  resmelted  in  the  blast-furnace,  a rather  un- 
desirable procedure.  Aside  from  this  flue-dust,  the  plant  has 
treated  at  times  considerable  quantities  of  concentrates  from 
stamp-mills,  and  accumulated  flue-dust  from  chlorination-plants, 
so  that  the  quantity  of  fines  was  really  more  than  the  furnace 
could  profitably  handle.  In  order  to  put  this  material  through 
and  keep  the  quantity  of  flue  dust  produced  within  limits,  the 
furnace  low  in  itself,  was  operated  with  a low  charge,  and  con- 
sequently with  a fairly  hot  top,  which  accentuated  the  losses  in 
fume.  The  flue-dust  increases  in  value  as  the  stack  is  ap- 
proached. 

Table  VIII. — Analysis  of  Flue-Dust, 


Material.  K,  203. 

Sl02. 

Lime. 

Sulphur. 

Copper. 

Gold. 

Silver. 

— * Per 

Per 

Per 

Per 

Per 

Oz.  Per 

Oz  Pei 

.Lent. 

Ce  t. 

Cent. 

Cent. 

Cent, 

Ion. 

Ton. 

From  dust-chamber . .. 

0.88 

1. 02 

4 1 

Beginning  of  Hue  (a) iC.14 

35*7 

4. 12 

5.60 

0.80 

1 17 

12.60 

Average  flue-dust(b) 2^.13 

34 

463(c) 

0.80 

1.25 

*3-55 

(a)  Contains  also  AI2O3  4.07  per  ( ent.  (b)  Contains  also  9 per  cent  carbon 

(c)  Considerable  of  which  is  Milan  * . n wat;  . 


Table  IX. — Analysis  of  Accretions  in  the  Dust-Chamber . 


Place. 

Curb  n. 

Copper. 

Gold. 

Silver. 

Per  Cent. 

Oz.  Per  Ton. 

Oz.  Per  Ton. 

From  the  bottom  of  downtake 

Considerable 

i4. 1 

0.70 

8.80 

On  the  blast-heat; ng  apparatus 

Considerable. 

16.  Ha) 

o.4o 

5-1 

(a)  All  soluble  in  water,  lor  the  most  part  being  present  in  the  form  of  copper  sulphate. 


17 

The  ratio  of  gold  to  silver  in  the  ore  is  usually  about  i to  2, 
so  that  the  analysis  of  the  accretions  shows  a heavy  loss  of  silver 
by  volatilization.  In  fact,  the  process  as  a whole  is  unfavorable 
to  a high  recovery  of  the  silver,  especially  if  high  concentration 
is  carried  on. 

LOSSES  IN  FUME—  It  has  been  the  experience  at  the 
National  Smelter  that  there  is  a considerable  loss  of  values  by 
smoke  and  fume,  especially  in  silver,  and  gold,  under  certain 
conditions;  as,  for  instance,  when  operating  with  high  concentra- 
tion and  lead  or  zinc  in  the  charge.  Lead  is  not  at  all  desirable 
in  the  furnace,  most  of  it  being  volatilized,  carrying  values  with 
it. 


Table  X. — Analysis  of  Condensed  Fume  from  the  National 

Smelter. 


Place  from  which  Taken. 

Gold. 

Silver 

Copper. 

Remarks 

Flue  near  the  s ack 

Oz.  Per  1 on 
1 5o 
i .6o 

1 .60 

2.00 

Oz  Per  l'on 
t5.5° 
it  90 

10.4® 

16,1 

1 er  Cent 
Trace 

Middle  of  flue 

Near  the  beginning  of  the 
flue 

'I  Contains  lead,  so  1 u b 1 e 

1 

suphates,  arsenic,  ?ome 

1 

J calcium  sulphate. 

Average  value  of  fume  from 
the  steel  roof  of  the 
flue 

The  analyses  show  the  relatively  much  greater  volatilization 
with  the  silver  suffers,  although  it  is  evident  that  the  gold  in  the 
ore  also  suffers  loss.  As  a matter  of  experience,  it  might  be  said 
that  when  the  furnace  is  running  low  with  a hot  top,  and  some 
of  the  above  mentioned  undesirable  elements  present,  the 
monthly  account  based  on  the  ore-assays,  will  show  a consider- 
able loss  in  silver,  and  a very  appreciable  one  in  gold,  as  well 
as  some  copper,  which  are  not  slag  losses.  Greater  attention 
paid  to  the  saving  of  fume  in  sulphide-smelting  plants  would 
lead  to  economy. 


Laboratory  Experiments  on  the  Unoxidized  Siliceous  Ores 
of  the  Black  Hills. 

By  Charles  H.  Fulton. 

It  is  well  known  that  while  the  ‘‘red”  or  oxidized  siliceous, 
or  Potsdam  ores  of  the  Black  Hills  yield  readily  from  75  to  85 
per  cent  of  their  gold  value  to  the  cyanide  process  as  at  pres- 
ent practiced  in  the  Hills,  the  “blue”  or  unoxidized  ores  yield 
but  from  30  to  50  per  cent  extraction,  and  are  as  a general  thing 
the  bugbear  of  the  millman.  Regirding  the  occurrence  of  the 
“blue  ores”  in  the  ore  bodies,  no  distinct,  line  can  be  drawn  sep- 
arating them  from  the  red  ores,  the  blue  ores  often  being  found 
in  bunches  and  pockets  in  the  red  ores,  in  widely  varying  quan- 
tities. The  amount  of  blue  being  mined  is,  however,  increasing 
as  the  workings  penetrate  further  into  the  ore  bodies.  This 
fact  is  amply  proven  by  the  extraction  figures  of  the  various  mills 
which,  as  a general  thing,  have  dropped  from  5 to  10  per  cent, 
within  the  last  two  years. 

While,  as  a usual  thing,  the  siliceous  ores  present  the  same 
general  characteristics  at  all  of  the  properties  yet  ores  from  the 
individual  mines  will  vary  quite  widely  as  regards  amenability 
to  cyanide  treatment.  The  ores  can  be  roughly  divided  into  two 
general  classes,  the  shale  ores  and  the  quartzite  ores,  of  which 
usaully,  though  not  invariably,  the  quartzite  ores  are  the  more 
refractory,  generally  on  account  of  their  greater  compactness 
and  density.  There  are  some  blue  ores  that  will  not  yield  more 
than  20  to  25  per  cent  of  their  values  to  ordinary  cyanide  treat- 
ment, while  others  will  yield  50  to  60  per  cent,  although  the 
latter  percentage  of  extraction  is  rare. 

The  gold  and  silver  values  are  very  evenly  distributed 
throughout  the  ores  as  is  shown  by  the  assay  of  different  screen 
sizes*.  It  is  rare  that  the  dust  has  a higher  value  than  the 
coarser  sizes,  and  it  sometimes  has  a lesser  value.  As  an  exam- 
ple, the  dust  accumulated  on  the  mill  rafters  from  the  dry 
crushing  of  ore  at  the  Imperial  mill,  had  a value  considerably 

*F.  C.  Smith.  The  Occurrence  and  Behavior  of  Tellurium  in  Gold  Ores, 
T.  A.  I.  M.  E.  Vol.  26,  p.  491.  Similar  Experiments  made  in  the 
laboratory  of  the  School  of  Mines  more  recently  confirm  these 
results. 


19 

less  than  that  of  the  ore  crushed  during  the  time  of  its  accumu- 
lation. These  facts  point  to  the  occurrence  of  the  gold  in  the 
ores  in  a comparatively  non-brittle  mineral.  Just  in  what 
form  the  values  do  occur  has  been  much  speculated  ont  but  it 
cannot  be  said  that  any  definite  conclusions  have  been  reached. 
It  seems  a rather  important  point  to  determine,  from  a metal- 
lurgical point  of  view,  as  having  an  influence  on  the  mode  of 
treatment.  F.  C.  Smith  states  that  he  has  found  tellurium  in 
many  of  the  Potsdam  ores,  and  believes  that  the  gold  occurs 
in  many  instances  as  sylvanite,  although  this  mineral  has  never 
been  isolated  except  in  ores  from  the  Ironsides  mine,  Squaw 
creek. t However,  the  fact  that  many  analyses  made  at  the 
School  of  Mines  recently,  fail  to  disclose  tellurium  or  but  traces 
of  it,  in  many  ores,  lead  to  believe  that  tellurium  is  not  of  such 
widespread  occurrence  in  the  siliceous  ores,  as  believed,  and 
that  the  gold  bearing  mineral  is  not  in  most  cases  a telluride. 
Experience  at  Cripple  Creek,  Colprado,  and  at  Kalgoorlie,  Aus- 
tralia, shows  that  the  dust  from  telluride  ores  invariably  runs 
higher  in  value  than  the  original  ore.  As  an  example,  a Crip- 
ple Creek  telluride  ore  shows  this  result:  t 

Original  ore  value  — 0.82  oz. 

Dust,  -f-  200  mesh,  value  =1.04  oz. 

Dust,  200  mesh,  value  =1.92  oz. 

This  is  due  to  the  extreme  sectility  of  the  telluridei'minerals. 
As  already  stated  the  dust  from  the  Black  Hills®' siliceous* *ore 
rarely  has  a higher  value  than  the  sands. 

It  has  also  been  found  that  a cyanide  solution  plus  ibromo 
cyanogen  exerts  a solvent  action  on  calaverite  and  possibly  sim- 
ilar telluride  minerals,  as  shown  by  results  on  a large  scale  at 
Kalgoorlie,  and  by  laboratory  tests  on  Cripple  Creek  telluride 
ores.  For  example:  A Cripple  Creek  ore  (Vindicator  mine) 
having  a value  of  1.09  oz.  gold,  gave  40.4  per  cent  extraction  on 
raw  ore  by  a 0.4  per  cent  cyanide  solution.  A 0.4  per  cent 
cyanide  solution  plus  bromo  cyanogen,  same  time  of  treatment, 
gave  91.7  per  cent.* 

fH.  M.  Change,  The  Discovery  of  New  Gold  Fields,  T.  A.  I.  M.  E,  Vol. 
29,  p.  229,  1033,  1037. 

fF.  C.  Smith,  T.  A.  I.  M.  E.  Vol.  29,  p.  1033. 

{Figures  furnished  by  Mr.  John  Millikin,  Dead  wood.  The  dust  men- 
tioned is  from  the  frame  work  of  a Cyanide  plant  at  Florence,  Col- 
orado. 

*For  data  concerning  Kalgoorlie  ores,  see  “Jhe  Diehl  Process”  by*  H. 
Knutzen,  T.  I.  M.  & M.  June,  1902. 


20 


An  extended  series  of  experiments  with  b'rcmo  cyanogen 
(results  of  which  follow)  on  the  “blue”  siliceous  ores  of  the 
Black  Hills  fail  to  show  such  phenomenal  results,  although  an 
increase  of  extraction  of  from  8 to  io  per  cent  is  noticeable. 

These  facts  certainly  throw  doubt  on  the  supposition  that 
the  gold  in  the  siliceous  ores  is  generally  in  the  form  of  a tellu- 


ride. 

Below  are  appended  a number  of  analyses  of  siliceous  ores, 
in  which  particular  attention  has  been  paid  to  the  elementary 
constituents  present  in  small  quantities  such  as  arsenic,  an- 


timony, etc. 

No.  i f 
(blue  ore.} 

Gold 0.63  oz.  per  ton 

Silver 2.00  “ 6 4 4 4 

Silica 65-38  per  cent  ... 

Iron 13-40  “ “ 

Sulphur ti.40  44 

Arsenic 0.90 

Antimony. ..  trace  

Tellurium. . .0.003 

Zinc ,0.00 

Copper .0  02.  

Manganese.. .trace 

Alumina..  5.43 

Lime 2.10 

Magnesia..  0.20 


No.  2.  f 
(blue  ore.) 
.0.85  oz  per  ton 
.6.08  4 4 4 4 4 4 

80.00  per  cent 

7.50  4 4 4 4 

.4.40  44 

2.00  4 4 4 1 


0.00 
.trace 
.0.00 
. 0.004 
.0.54 

.1.79 

1.70 

.not  determined 


No.  3d 
(blue  ore.) 

Gold 3.35 

Silver 1.7s 

Silica....  80.90 

Iron 9.94 

Sulphur .4.53 

Arsenic 0.29 

Antimony. ...  trace 

Tellurium . . ..0.007 

Copper 0.013 

Zinc tra^e 

Manganese. . Lace 

Alumina 1.70 

Lime 0.5°  per  cen‘ . . . 

Magnesia. . . .trace 

Ore  ‘‘A-’ 

No.  5. 

( blue  ore.) 

Gold 0.78  oz,  per  ton 


No.  4.t 

(partially  oxidized  )f 

2.00 

0.62 

84.80 

7-50 

0.7s 

0.00 

0.00 

trace 

0.008 

0.00 

0.96 

T 02 

0.90  per  cent 

not  determined 

Ore  44B” 

No.  6. 

( blue  ore.) 
0.90  oz.  per  ton 


fKindly  furnished  by  Mr.  John  Gross,  Maitland,  S.  Dak. 


21 


Silver 

Silica . 

77.38.. 

T ron 

Sulphur. . . . 

Arsenic 

.0.55.. 

Antimony..  • 

. trace. 

Telhirium . . 

. .none, 

Copper 

Manganese. 

.none. 

Alumina  . . . 

Lime 

.0.56. . 

Magnesia. . . 

.trace. 

Phos.  acid . . 

..0.32. . 

Soda 

..1.32. . 

Lead 

Thallium. . . 

. ? 

Tungsten. . . 

. . . 

93*72  per  cent 
.2.67  “ “ 

.o.6g  “ “ 

.0.002 
.0.0893 
.none 
.none 
0.082 

..3. 33  per  cent 


.0.0059 

.trace 

p 

none 


In  the  analyses,  copper,  antimony,  arsenic,  tellurium,  will 
be  noticed  in  small  quantities  in  most  of  the  ores.  In  the  Mait- 
land ores  bismuth  also  exists  in  appreciable  quantities  for  at  the 
Penobscot  mill  it  is  found  in  considerable  amounts  in  the  zinc 
precipitates.  Certain  peculiar  facts  are  noticed  in  roasting;  var- 
ious blue  ores,  as  a general  thing  a fair  extraction  may  be  ob- 
tained on  most  of  the  blue  ores  if  they  be  finely  crushed  and 
roasted  at  a low  heat  for  a considerable  time.  If  the  heat  be 
raised  to  a high  temperature  at  once,  with  some  ores  but  little 
better  extraction  can  be  obtained  than  from  the  raw  ore.  Other 
blue  ores  again  do  not  behave  in  this  way.  It  seems  possible 
that  the  gold  and  silver  are  held  in  some  complex  mineral  com- 
bination into  which  arsenic  and  antimony  enter,  so  that  a high 
temperature  and  oxidizing  conditions  transform  this  compound 
into  stable  compounds,  failing  to  liberate  the  gold  and  silver. 
The  gold  and  silver  bearing  mineral  is  also  very  uniformly  dis- 
tributed throughout  the  rather  dense  ores,  so  that  in  most  in- 
stances a comparatively  fine  crushing*  is  required  to  liberate  the 
values  from  the  rock  mass.  Roasting  of  the  ores  causes  practi- 
cally no  loss  of  values. 

The  fact  that  the  siliceous  ores  of  the  Black  Hills  were  pos- 
sible telluride  ores  led  to  the  rather  extended  series  of  experi- 
ments with  bromo  cyanogen,  which  while  not  giving  the  results 
hoped  for,  aid  the  extraction  of  the  values  somewhat,  so  that 
the  publishing  of  the  results  seems  justified.  All  the  tests  made 
were  agitation  bottle  tests,  which,  is  the  usual  starting  point  in 


*There  are  exceptions  to  this  rule,  as  for  instance,  certain  ores  of  the 
Wasp  No.  2 mine,  and  the  Ragged  Top  ores. 


22 


experiments  of  this  kind.  The  results  obtained  by  these  were 
to  be  confirmed  by  tests  on  a larger  scale,  but  unfortunately  the 
time,  means  and  apparatus  for  this  work  was  not  available.  The 
tests  were  made  practically  all  on  the  ‘ ‘blue  ores”  with  the  idea  that 
the  more  oxidized  ores  would  be  tested  later.  The  effect  of  bromo 
cyanogen  on  the  extraction  is  soon  to  be  tried  on  a large  scale  by 
one  or  two  of  the  mills  of  the  district,  and  the  results  will  be 
watched  with  great  interest. 

BROMO  CYANOGEN — Bromo  cyanogen  and  chloro-cy- 
anogen  were  first  used  unsuccessfully  in  the  Cyanide  process  by 
Dr.  William  H.  Gaze,  in  Australia  in  1892.  Later  in  1894  the  use 
of  bromo  cyanogen  was  patented  by  Messrs.  Sulman  and  Teed 
in  connection  with  zinc  dust  precipitation  in  England.  It  is  at 
present  used  in  Kalgoorlie,  West  Australia,  in  the  Diehl  process 
with  success,  on  sulpho  telluride  ores.t 

Bromo  Cyanogen  above  a certain  temperature  is  a pun- 
gent irritating  colorless  vapor,  extremely  poisonous  which 
affects  the  eyes  and  lungs  in  a very  irritating  manner.  At  60  °C 
it  sublimes  into  colorless  needles,  which  afterwards  change  to 
cubes.  The  vapor  and  sublimate  is  soluble  in  water  and  methyl 
alcohol,  more  so  in  alcohol  than  in  water. 

When  heated  in  a closed  tube  to  140  °Cit  is  converted  into 
CN3  Br3.  It  is  decomposed  by  potassium  cyanide  with  the  fol- 
lowing reaction. 

KCN  + BrCN  = KBr  + 2CN. 

With  alkalies  such  as  potassium  hydrate,  the  following  re- 
action probably  takes  place  in  dilute  solution. 

BrCy  + 2KOH  = KBr  + KCNO  + H2O. 

PREPARA  TION  OF  BROMO  CYANOGEN—  There  are 
three  methods  of  preparing  bromo  cyanogen. 

1.  By  the  Addition  of  Dilute  Bromine  Water  to  a Dilute 
Solution  of  Potassium  Cyanide , the  Last  Being  in  Excess — The 
amounts  of  bromine  and  cyanide  are  best  present  in  the  theo- 
retical quantities  expressed  by  the  reaction. 

fThe  Diehl  Process,  H.  Knutzen,  T.  I.  M.  & M.  June  1902. 

Metallurgical  Progress  in  W.  Australia,  E.  & M.  Jour.  Vol.  75,  p.  18,251, 
also  Vol.  77,  p.  31. 

The  Treatment  of  Sulpho-telluride  ores  at  Kalgoorlie,  E.  & M.  Jour. 
Vol.  76,  p.  156. 

The  Treatment  of  Telluride  ores  by  Dry  Crushing  and  Roasting  at 
Kalgoorlie,  T.  I.  M.  & M.  Oct.  15,  1903. 

Cyanide  Practice,  by  Alfred  James,  1903, 


1 


23 

2 Br  + KCN  = KBr  + BrCN. 

The  bromine  water  may  be  added  until  a faint  permanent 
yellow  color  appears.  The  cyanide  solution  during  the  addition 
of  bromine  water  should  be  kept  cold  by  ice  water,  as  the  heat 
developed  by  the  reaction  is  sufficient  to  drive  off  the  bromo 
cyanogen  as  a vapor  from  the  solution. 

2.  Preparation  by  Means  of  Bromine  and  Mercuric  Cyan- 
ide.— When  one  part  of  liquid  bromine  is  allowed  to  flow  grad- 
ually on  2 parts  of  mercuric  cyanide  (dry  salt)  in  a retort*  sur- 
rounded by  ice,  bromo  cyanogen  and  mercuric  bromide  are 
formed  with  a great  evolution  of  heat.  Bromo  cyanogen  sub- 
limes in  needles  contaminated  with  free  bromine,  which,  however, 
flows  back  into  the  retort  and  enters  into  complete  combination. 
Gentle  heat,  by  means  of  an  alcohol  lamp,  is  then  applied  and 
the  BrCN  sublimed  into  a receiver  surrounded  by  ice  water. 

Mercuric  cyanide,  if  not  available,  can  be  made  by  dissolv- 
ing mercuric  oxide,  (which can  be  made  from  mercury  or  mer- 
curic nitrate)  in  a solution  of  hydrocyanic  acid.  The  hydrocy- 
anic acid  can  be  made  with  potassium  Ferro  cyanide  or  potas- 
sium cyanide  and  dilute  sulphuric  acid,  by  heating  in  a dis- 
tilling bottle  and  collecting  the  vapor  in  ice  water,  or  water 
cooled  by  ice.  When  the  mercuric  oxide  is  all  dissolved  in  the 
hydrocyanic  acid  solution  in  the  cold  it  is  gently  evaporated 
to  crystals  on  a water  bath,  care  being  taken  not  to  remove  the  very 
last  of  the  solution  on  the  bath,  but  to  let  it  evaporate  in  the  air, 
or  in  an  air  bath  at  a temperature  not  exceeding  1200  Fahr  , 
otherwise  there  is  danger  of  reducing  the  mercuric  cyanide. 

Bromo  cyanogen  crystals  obtained  in  this  way  can  be  kept 
in  a tightly  corked  bottle  in  a cold  place  for  use  indefinitely. 
This  method  is  the  most  difficult  and  expensive  method  of  prep- 
aration, but  yields  the  pure  crystals  of  bromo  cyanogen  unadult- 
erated by  any  other  salt.  This  may  sometimes  be  desirable  for 
certain  tests,  but  for  general  experimental  purposes  bromo  cy- 
anogen made  by  the  first  method,  or  still  better  by  the  third 
method,  to  be  described,  which  is  the  commercial  method  of  its 
production  in  Western  Australia,  is  just  as  desirable. 

3.  Preparation  by  Means  of  Bromine  Salts , Potassium 
Cyanide  and  Sulphuric  Acid.—  When  solutions  of  potassium 

*The  apparatus  for  this  work  is  best  a small  retort  and  receiver,  the  re- 
tort having  an  openingfor  a small  thistle  tube  with  stop  cork  for  the 
introduction  of  brome.  See  Denver  Fire  Clay  catalogue,  p.  173, 
No.  1313. 


24 

bromide,  potassium  bromate,  potassium  cyanide  and  sulphuric 
acid  are  mixed  in  the  proper  proportions,  bromo  cyanogen  in 
solution  is  produced  according  to  the  following  equation: 

2KBr  + KBrOs  + 3KCN  + 3H2SO4  = 3BrCN  + K2SO4  + 3H2O 

238  167  135  294  318  522  54 

1.42  1 1. 1 7 1.76  1.90 

It  is  essential  for  success  that  the  proportions  of  the  theo- 
retical equation  be  followed  closely  and  that  the  solution  be 
not  too  concentrated. 

TO  TAKE  A DEFINITE  EXAMPLE: 

Taking  as  the  starting  point  2 5 grms.  of  potassium  bromate 
it  will  require  1.42  x 25  = 35. 5 grms.  of  potassium  bromide 

1.17x25=29.25  “ “ “ cyanide 

1 76x25=44.0  “ “ sulphuric  acid. 

This  should  produce  47. 5 grms.  of  bromo  cyanogen.  The  Po- 
tassium bromide  and  bromate  may  be  dissolved  in  about  400 
c.  c.  of  cold  water.  It  will  take  some  time  to  disolve  the  bro- 
mate, as  it  is  rather  difficultly  soluble  in  water.  The  potassium 
cyanide  can  be  dissolved  in  200  c.  c.  of  water,  and  the  required 
amount  of  sulphuric  acid  diluted  to  400  c.  c. 

The  strength  of  the  sulphuric  acid  should  be  estimated  be- 
fore dilution  with  an  N-10  solution  of  sodium  hydrate,  4 grams 
to  the  litre,  one  c.  c.  of  which  is  equivelant  to  .0049  grams  of 
sulphuric  acid.  The  proper  amount  of  sulphuric  acid  being* 
taken,  containing  44  grins.,  this  is  diluted  to  400  c.  c.  and  al- 
lowed to  cool  thoroughly.  In  taking  the  amount  of  cyanide, 
care  must  be  taken  to  allow  for  the  amount  of  impurity  in  the 
salt. 

The  solutions  of  potassium  bromide,  bromate,  cyanide  and 
of  sulphuric  acid  are  now  mixed  best  by  pouring  the  bromine 
salts  and  cyanide  solutions  simultaneously  in  a thin  stream  into 
a large  funnel  discharging  into  a bottle  containing  the  sulphuric 
acid.  It  is  essential  to  mix  in  this  way  Otherwise  reactions  oc- 
cur which  occasion  loss.  The  best  way  is  to  have  the  two  solu- 
tions discharging  simultaneously  in  a thin  stream  from  large 
stop  cock  funnels. 

After  the  mixing  of  the  solutions  the  resultant  solution 
should  be  agitated  for  about  six  hours  to  complete  the  reactions. 
The  solution  is  then  ready  for  use,  and  will  contain  about  4/4 
per  cent  of  bromo  cyanogen  (theoretically  in  this  example  4.75 
per  cent. ) 


25 

Pure  potassium  bromate  is  a rather  expensive  salt,  $2.00 
per  pound  if  bought  in  small  quantities  (although  in  large  quan- 
tities it  can  be  had  at  about  50c  per  lb.),  and  in  practice  as  men- 
tioned further  on  commercial  mixed  bromine  salts  are  used. 
For  experimental  purposes  the  mixed  bromide  and  bromate 
salts  can  readily  be  made  in  the  laboratory  by  the  addition  of 
liquid  bromine  to  a saturated  solution  of  potassium  hydrate. 
This  solution  after  the  addition  of  bromine  is  heated  until  the 
bromine  disappears,  when  more  bromine  is  added,  this  being  re- 
peated until  the  red  color  stays  permanently.  The  solution  now 
contains  a 'mixture  of  potassium  bromide  and  bromate  from 
which  the  bromate  containing  some  bromide  will  separate  out 
first  when  the  solution  cools,  owing  to  its  inferior  solubility. 
This  can  readily  be  removed  by  filtration  and  the  solution  evap- 
orated to  the  dry  salts. 

The  reaction  for  the  preparation  of  bromo  cyanogen  calls 
for  a mixture  of  bromide  and  bromate,  of  which  41.2  per  cent 
should  be  potassium  bromate.  If  the  solution  containing  the 
mixed  salts  made  in  the  way  described  be  evaporated  down  to 
dry  salt,  the  mixture  will  contain  considerably  less  than  4.12 
per  cent  of  bromate.  For  this  reason  it  is  desirable  to  remove 
successively  the  salt  which  settles  out  from  the  solution  on 
evaporation  and  which  is  at  first  practically  all  bromate  but 
gradually  decreases  in  this  salt  until  what  precipitates  finally  is 
practically  only  bromide.  In  this  way  by  having  lots  of  salts, 
some  high  in  bromate  and  others'  in  bromide,  the  proper  mixture 
of  the  two  salts  can  readily  be  made  especially  if  some  extra 
potassium  bromide,  a common  saU  in  the  laboratory,  be  at  hand. 

The  resultant  solution  should  be  neutral,  as  bromo  cyanogen 
shows  neutral  to  methyl  orange  and  phenolpthalein,  but  may  be 
slightly  acid  owing  to  the  reactions  being  incomplete.  If  it  should 
be  acid,  this  acidity  must  be  carefully  neutralized  by  an  N-10 
potassium  or  sodium  hydrate  solution,  care  being  taken  not  to 
add  any  excess,  as  this  alkali  decomposes  bromo  cyanogen,  as 
already  mentioned. 

The  bromo  cyanogen  solution  prepared  in  this  way  is  quite 
stable  and  keeps  a considerable  length  of  time,  several  months,  _ 
if  kept  in  a tightly  stoppered  bottle.  It  may  turn  a brown  color 
upon  standing,  which  color  is  not  due  to  free  bromine.  This 
color  does  not  interfere  with  the  reactions. 

Bromo  cyanogen  is  made  on  a commercial  scale,  in  West- 
ern Australia  at  Kalgoorlie  as  follows:* 


* A.  James,  E.  & M.  Jour.  Vol.  77.  p.  31. 


26 


It  is  made  from  imported  salts  (Germany)  which  contain  ap- 
proximately 40  per  cent  of  potassium  bromate  and  the  balance 
bromide.  At  Kalgoorlie  to  generate  100  lbs.  of  bromo  cyanogen 
the  following  charge  is  used: 

Mixed  bromo  salts,  125  lbs. 

Cyanide,  100  percent  65 

Sulphuric  acid,  70  per  cent  147 

The  bromo  cyanogen  is  made  in  a wooden,  plain  or  lead 
lined  vat  of  about  200  gals.’  capacity,  securely  covered  with  a 
lid  through  which  a revolving  paddle  or  stirrer  works,  Above 
this  vat  is  a smaller  vat  in  which  is  stored  the  necessary  charge 
of  potassium  cyanide  dissolved  in  40  gals,  of  water.  The  mixing 
vat  is  first  three-quarters  filled  with  water,  the  agitator  is  started 
and  the  sulphuric  acid  added  slowly  and  carefully.  The  whole 
is  now  left  to  stand  and  cool  for  one  or  two  hours,  as  the  heat 
generated  by  the  addition  of  sulphuric  acid  would  vaporize  the 
bromo  cyanogen  were  the  rest  of  the  ingredients  added  at  once. 
When  the  contents  of  the  vat  are  cool  the  mixed  bromo  salts  are 
added  gradually  and,  simultaneously  the  solution  of  cyanide  is 
run  in  with  constant  stirring.  The  reaction  commences  imme- 
diately, but  is  not  thoroughly  completed  until  six  hours  of  con- 
tinuous agitation. 

The  resultant  bromo  cyanide  solution  is  then  added  in  the 
quantities  desired  to  the  agitation  vats. 

• METHODS  OF  ESTIMATING  THE  AMOUNT  OF 
BROMO  CYANOGEN  AND  POTASSIUM  BROMATE.— 
For  the  quantitative  estimation  of  both  potassium  bromate  and 
of  bromo  cyanogen  an  N-10  solution  of  sodium-thio-sul- 
phate  will  answer.  This  solution  will  contain  12.4  grams  of  the 
salt.  (Na2S203. 5H2O)  and  1 c,  c.  will  be  equivalent  to 
0.00265  grms.  of  bromo  cyanogen, 

0.00142  “ “ potassium  bromate. 

For  the  Estimation  of  Potassium  Bromate  in  the  mixed  salts 
of  bromide  and  bromate  proceed  as  follows: 

Weigh  out  200  milligrams  of  the  dry  salt,  dissolve  in  100  c.c. 
of  distilled  water,  then  add  about  15  to  20  c.  c.  of  dilute  hydro- 
chloric acid,  and  3 to  5 grms.  of  potassium  iodide.  Iodine  will 
be  liberated  and  the  solution  is  then  titrated  to  colorlessness  by 
N-10  sodium-thio-sulphate  solution.  If  greater  accuracy  is  re- 
quired starch  solution  can  be  used  as  an  indicator. 

The  reaction  taking  place  is  as  follows: 


27 

KBrC>3  + 6KI  -f-  3H2SO+  = 3K2  SOi  -f-  KBr  3I2  -(-3H2O 
or  KBrC>3  = 3I2 

I2  — 2 (Na2S203. 5H2O)  = Naz  S* *  Og  H-  2NaI  ~b  10H2O 

For  the  Estimation  of  Bromo  Cyanogen  take  5 to  10  c.  c.  of 
the  solution  to  be  titrated,  dilute  with  25  to  50  c.  c.  of  water, 
add  5 c.  c.  of  dilute  hydrochloric  acid  and  4 to  5 grams,  of  potas- 
sium iodide.  This  liberates  iodine  and  the  solution  is  titrated  to 
colorlessness  by  N-10  sodium-thio-sulphate  solution.  Or  as 
above,  starch  solution  can  be  used  as  an  indicator. 

The  reaction  taking  place  is  as  follows: 

BrCN  -f  2KI  + 2HCI  ='  BrCN  + 2HI  -f  2KCI 
BrCN  4-  2HI  = HBr  + HCN  + I2 

I2  “| — (Na2S203.5H2  O)  ==  Na2S*OG  4-  2 Nal  4~  10H2O. 

In  estimating  mill  solutions, or  solutions  that  have  been  used 
on  ores  experimentally,  and  which  contain  potassium  cyanide, 
the  presence  of  this  salt  does  not  interfere  with  the  titra- 
tion for  bromo  cyanogen  and  in  the  estimation  of  potassium 
C3ranide  in  these  same  solutions  with  silver  nitrate  in  the  usual 
way,  bromo  cyanogen  does  not  interfere  with  the  test  except  in 
so  far  as  cyanogen,  which  may  be  present,  due  to  the  reactions 
between  bromo  cyanogen  and  potassium  cyanide,  interferes. 

Usually  the  presence  of  cyanogen  gives  somewhat  low  re- 
sults.t 

* METHOD  OF  MAKING  BROMO  CYANOGEN 
TESTS  ON  ORES . — In  experimental  work  the  general  prac- 
tice is  to  add  bromo  cyanogen  in  solution  to  the  test  at  in- 
tervals of  2 to  4 hours,  the  total  amount  of  bromo  cyanogen 
not  to  exceed  one-fourth  the  amount  of  the  potassium  cyanide 
present  in  the  experiment.  As  an  example,  suppose  16  assay 
tons  of  ore  are  treated  with  700  c.  c.  of  a 0.25  per  cent,  or  5 
pounds  per  ton  potassium  cyanide  solution,  containing,  therefore, 
1.75  grams  of  cyanide.  The  total  amount  of  bromo  cyanogen 
to  be  added  to  this  test  is  therefore  0.44  grams,  and  having 
a 3 per  cent  bromo  cyanogen,  solution  each  cc.  containing 
.03  grms.  the  total  number  of  c.c.  to  be  added  of  this  solution 
will  be  15.  If  we  make  three  additions  at  intervals  of  4 hours, 
each  we  will  add  5 c.  c.  each  time. 

The  theory  of  the  reactions  with  bromo  cyonogen  is  as  fol- 
lows: 

f James,  Cyanide  Practice,  1902,  p.  140. 

* James,  “ “ 1902,  chapter  on  Bromo  Cyanogen. 


28 


BrCN  + KCN  = KBr  + 2CN. 

Au  + KCN+  CN  = KAuCN2. 

The  bromo  cyanogen  acts  as  a liberator  of  cynogen  thus  prac- 
tically taking  the  place  of  oxygen  in  the  ordinary  process.  The 
nascent  cyanogen  acts  as  a hastener  of  the  reaction  and  it  is 
also  probable  that  bromo  cyanogen  plus  potassium  cyanide  may 
have  a more  powerful  solvent  action  on  certain  gold  minerals, 
such  as  calaverite,  than  the  simple  cyanide  solution. 

The  idea  of  adding  bromo  cyanogen  in  small  amounts  from 
time  to  time  is  to  have  the  liberation  of  cyanogen  going  on  dur- 
ing the  entire  treatment.  The  greater  the  amount  of  potassium 
cyanide  present  in  proportion  to  the  bromo  cyanogen  the  more 
rapid  is  the  decomposition  of  the  latter.  With  additions  of 
bromo  cyanogen  as  described  in  the  test  above,  there  will  prob- 
ably be  no  bromo  cyanogen  left  in  the  solution  after  the  ex- 
piration of  3 or  4 hours.  Any  bromo  cyanogen  left  in  solution 
after  the  expiration  of  the  time  of  agitation  is  of  course  a waste 
and  in  tests  following  the  amount  may  be  cut  down  somewhat  if 
this  should  be  the  case. 

The  consumption  of  potassium  cyanide  is  greater  with  bromo 
cyanogen  than  without,  and  this  must  be  taken  into  account  in 
experimenting,  not  using  too  dilute  solutions,  especially  in  agita- 
tion tests  in  which  consumption  is  abnormally  high. 

The  solutions  from  the  tests  are  very  often  a light  brown  or 
golden  color,  due  probably  to  iron  bromide,  for  more  iron  salts 
go  into  solution  with  bromo  cyanogen  than  with  plain  cyanide. 
The  earlier  writerst  dwelt  at  length  on  difficulties  of  precipitat- 
ing the  gold  from  the  solutions  when  bromo  cyanogen  is  em- 
ployed, stating  that  bromo  cyanogen  has  a decided  action  on 
zinc  forming  insoluble  zinc  bromo  and  zinc  cyanide,  which  in- 
terferes with  the  precipitation.  In  the  present  state  of  the  pro- 
cess there  should  be  no  bromide  cyanide  in  the  solution  when  it 
it  goes  through  the  zinc,  ; s it  should  be  all  decomposed.  This 
difficulty  in  precipitation  seems  not  to  be  encountered  in  West 
Australia,  where  bromo  cyanogen  is  used  extensively.. t 

COST  OF  BROMO  CYANOGEN  — The  mixed  salts  of 
potassium  bromide  and  bromate,  containing  approximately  40 
. - 

fGaze — Practical  Cyanide  Operations,  7898,  p.  95. 

fFor  certain  minor  troubles  of  precipitation, see  “Treatment  of  Telluride 
ores  by  Dry  Crushing  and  Roasting  at  Kalgoorlie,  W.  A.,  W.  E. 
Sampson.,  T.  I.  M.  & M.  Oct.  1903. 


29 

per  cent  of  the  latter  salt  3anbe  readily  obtained  in  this  country* 
and  can  be  delivered  in  500  pound  lots  packed  in  barrels  f.  o.b. 
Deadwood  at  25c  per  pound.  Sulphuric  acid  costs  at  Dead- 
wood  from  2.6c  to  3c  per  pound  and  potassium  cyanide  23c  per 
pound. 

The  cost  per  pound  for  chemicals,  in  making  bromo  cyano- 
gen will  therefore  be,  taking  the  Western  Australia  charge  as  a 


basis: 

125  pounds  mixed  bromo  salts  at  24c  per  lb.  = $30.00 

65  pounds  of  potassium  cyanide  at  23c  per  lb.  =14  .95 

147  pounds  of  70  per  cent  sulphuric  acid  at  3c=  4.41 


Total  cost  100  lbs.  cyanogen  49. 36 

Cost  per  pound  = . 50 


The  cost  of  labor,  power,  etc.,  of  making  may  be  estimated 
at  5c  more,  making  a total  cost  of  55c  per  pound. 

The  following  tables  show  concisely  the  results  obtained  and 
the  details  of  the  experiments  on  the  blue  siliceous  ores  of  the 
Black  Hills.  The  ores  are  taken  from  the  various  districts, 
Bald  Mountain,  Ruby  Basin,  Maitland  and  Yellow  Creek,  so  as 
to  give  a representation  of  most  of  the  blue  ores. 

*Can  be  bought  from  the  Dow  Chemical  Company,  at  Midland,  Michi- 
gan. 


'i 


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Table  IV. 

ORE  “D”— A very  dense  blue  ore,  containing  .22  oz.  per  ton.  Tests  made  on  5 to  8 oz.  lots,  amount  of  solution  300  to 


Table  I. 

ORE  "A”-A  dense  blue  silicious  ore,  containing  0.78  oz.  gold  per  ton.  For  analysis,  see  previous  pages.  Tests 
made  on  5 to  8 oz.  lots,  amount  of  solution  300  to  500CC.  


Number. 

I Ore  p ssed  a 

I Screen  of  the 

following  mesh: 

Strength  of  Cy- 

anide Solution. 
Pounds  per  ton. 

Method  of  Treatment. 

Amount  of 

BrCN 

Added. 

Time  of  Treatment. 

Cyanide  Con- 

sumption in  lbs. 
per  ton. 

Assay  of 

Tails. 

oz.  per  ton. 

Pei  cent 
of 

Extraction 

1 

20  mesh 

20 

Plain  Cyanide,  no  alkali  added. 

36  hours  agitation 

4.9 

0.5a 

33.3 

2 

40  mesh 

20 

Plain  cyanide,  no  alkali  added. 

36  hours  agitation 

4.9 

0.47 

39.7 

3 

150  mesh 

,0 

Plain  cyanide,  ore  treated  12  hours  with  KOH. 

previous  to  cyaniding. 

60  hours  agitation 

2.6 

°-35 

55-1 

4 

200  mesh 

IO 

Same. 

60  hours  agitation  i 

2.9 

0.36 

53.8 

5 

40  mesh 

20 

Plain  cyanide,  with  addition  of  small  amount 
of  lead  acetate. 

60  hours  agitation 

12.7 

0.41 

47.4 

6 

80  mesh 

20 

Same. 

41  hrs,  agitation  and  31  days 
standing 

13.3 

037 

52-5 

7 

150  mesh 

30 

Same. 

Same 

•.36 

53-8 

8 

40  mesh 

IS.  1 

Cyanide  and  bromo-cyanogen. 

7add’sof3>i 

c.c.  Ea.  of  a. 
3.3  perct.sol 

Same 

4., 

o.4i 

47;4 

9 

80  mesh 

15.1 

Same. 

Same 

22X  hours  agitatioa 

4-7 

o.4o 

46.1 

1 O 

150  mesh 

IS. I 

Same. 

Same 

22H  hours  agitation 

4.7 

0-39 

44.8 

1 1 

40  mesh 

10.6 

Same. 

6 add's  of  4 0.0. 

ea.  of  a 3.5  per 
oent  sol. 

22K  hours  agitation 

7-5 

0.42 

48.7 

1 2 

80  mesh 

»o.6 

Same. 

Same 

4o  hours  agitation 

7-5 

0.4 1 

47.4 

1 3 

150  mesh 

10.6 

Same. 

Same 

40  hours  agitation 

7-5 

0.40 

46.1 

1 4 

40  mesh 

20.0 

Same. 

0.98  grms  in 
3 additions. 

40  hours  agitation 

*14.0 

0.39 

44.8 

1 5 

80  mesh 

20.0 

Same. 

Same 

41  hours  agitation 

*13.8 

o.41 

47.4 

16 

150  mesh 

20.0 

Same, 

Same 

4i  hours  agitation 

*10.5 

o.37 

Sz-5 

1 7 

150  mesh 

xo.6 

Cyanide  and  bromo-cvanogen;  ore  treated  with 
KOH.  12  hours  before  cyaniding. 

6 adds.ef  4o.c. 
ea  of  a 3.8  per 
oent  sol. 

60  hours  agitation 

3-1 

0.28 

64.1 

1 8 

200  mesh 

xo.6 

Same. 

Same 

60  hours  agitation 

4*2  . 

O.3O 

6r.5 

1 9 

130  mesh 

8.9 

Roasting,  cyanide  and  bromo-cyanogen. 

Same 

48  hours  agitation 

5-1 

o.xo 

87.1 

20 

150  me  h 

xo.o 

Same, 

4 adds,  of  4 o. 

c.  ea.  of  a 3.J 
per  cent  sol. 

1 24  hours  agitation 

,8 

0.19 

75.6 

2 1 

150  mesh 

10.0 

Same. 

6 adds,  of  4 c. 
c.  ea.  of  a 5 pei 
cent  sol, 

j 44  hours  agitation 
r } 48  hours  standing 

0.14 

82.0 

22 

150  mesh 

xo.o 

Roasting, cyanide  & bromo  cyanogen;  ore  treal 
edwith  KOH  for  12  hours  before  cyaniding. 

l 

Same 

Same 

o.il 

85.8 

23 

150  mesh 

,0.0 

Roasting  and  plain  cyanide;  ore  treated  witfc 
KOH,  for  i2  hours  before  cyaniding 

i 

Same 

o- Is 

80.7 

24 

150  mesh 

xo.o 

Roasting  and  plain  cyanide. 

Same 

0.14 

82.0 

26 

150  mesh 

10. 0 

Same. 

24  hours  agitation 

i-5 

0.I9 

75.6 

26 

150  mesh 

8.9 

Same. 

48  hours  agitation 

1.4 

0.19 

75.6 

♦Excessive  consumption  due  to  impure  bromo-cyanogen. 


ORE  “B.”  A dense  blue  ore,  containing;  o.go  oz.  gold  per  ton.  For  analysis  see  previous  pages. 
Tests  mode  on  2 to  5 oz.  lots,  amount  of  solution  200  to  400  cc. 


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Table  III. 

ORE  “C.”  A dense  blue  ore,  containing  more  sulphur  than  A.  or  B.,  containing  0.66  oz.  of  gold  per  ton. 
Tests  made  on  3 to  5 oz.  lots,  amount  of  solution  300  to  500  cc 


Miscellaneous  tests.  In  the  main  to  show  efficiency  of  broinc-  yanogen  on  certain  ores.  Tests  made  on 
lots,  amount  of  solution  300  to  500  cc. 


3 


Percentage 

N 

rc 

| O 

| c 

O 

O 

of 

H 

M 

CO 

o 

O 

0 

0 

O 

Extraction. 

o> 

00 

O' 

M 

1 M 

w 

K 

Assay  ■ f 

O' 

1 

tJ- 

O 

O 

Heads 

0 

"c 

10 

lO 

iG 

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SUMMARY  OF  EXPERIMENTS. — Influence  of  the 
fineness  of  crushing.  The  size  of  the  ore  is  stated  by  “mesh”  in 
the  tables  which  means  that  the  ore  passed  an  ordinary  assayers 
screen  of  the  mesh  stated.  For  further  information  the  actual 
size  of  openings  or  space  and  size  of  wire  of  these  screens  is 
given. 


Screen.  Number  of  Meshes 
per  inch. 

Decimal  size  of  wire  in 
inches. 

Actual  Opening  between  wires  or  ‘pace 
in  inches. 

20 

0.0I65 

0 0335 

3o 

°-OI375 

0.0195 

40 

0.01025 

0.01475 

80 

0.00575 

IO 

VO 

O 

O 

6 

150 

0.003 

c.0033 

200 

0.002 

0 003 

Material  called  30  mesh  was  sized  and  gave  the  following 
results: 


Per  cent  left  on  a 40  mesh  screen 
“ “ “ “ 60  “ 

80 
‘Too 

4 4 4 4 4 4 4 4 4 4 4 4 

150 

“passed  through  a 150 


= IO-4  I 

= 29.8  I coarser  than  100  mesh 
— 16.7  f 66.1  percent. 

finer  than  100  mesh 
33.8  per  cent. 


= 9-2  | 

= 1 1-7  ) 
= 22. 1 V 


Total  100.0 


In  order  to  show  how  this  product  compares  to  actual  mill 
products  made  in  the  Black  Hills  the  following  figures  are  ap- 
pended: 


PRODUCT  OF  A S'X  FOOT  MONADNOCK  ROLLER 
MILL. — Screen,  wire  cloth  with  space  of  0.046  inches,  equiva- 
lent to  18  mesh. 


Per  cent  left  on  a :o  mesh  screen  = 1 per  cent  | 


“ passed  a 


‘40 

= IO 

11  coarser  than  100 

‘60 

= 1 O 

( mesh  31  per  cent. 

Too 

= lO 

;;  1 

‘200 

---  19 

\ finer  than  100 

200 

=r  50 

) mesh  69  per  cent 

Total  100.  per  cent. 

PR0DUC1  OF  STAMPS. — Weight,  950  lbs.  Screen  10  by 
4 mesh  No,  18  wire,  space  0.053  inches.  Dakota  mill,  Deadwood. 


33 

Per  cent  left 

on  a 20  mesh 

screen  = 12.7 

) 

it  < < < « 

40 

— 22.0 

)-  coarser  than  100  mesh 

“ 

“ “ 80  “ 

— 14S  J 

1 55.5  percent. 

“ “ 

“ 100 

= 6.0 

1 

it  < . « < 

“ “ 150  “ 

= 14.8 

>*  finer  than  100 

“passed  thro’i5o 

“ =-29.8) 

44.6  per  cent. 

Total 

100.0 

PRODUCT  OF  DRY  CRUSHING  ROLLS.— Imperial 
mill,  passed  through  a 16  mesh  wire  screen,  21  wire  space  .0305 
inches. 


Per  cent  left  on  a 20  mesh 
“ 3Q 
“ 40 

“ “ “ “ 60  “ 

“ “ “ “ 80  “ 

“ 100 

passed  a 100 


screen 


coarser  than  100  mesh 
64  per  cent. 


finer  than  100  mesh 
36  per  cent. 


Total  100 

The  effect  of  the  size  of  ore  on  the  extraction  is  shown  as 
follows,  the  results  being  averages  of  tests  made  under  same 
conditions: 


Mesh. 

Ore  A . 

Ore  B. 

Laboratory  Screen. 

4o 

46.9  per  cent. 

62.2  per  cent . 

80 

46.9  “ 

64.4  “ “ 

150 

47.8  “ “ 

64.4  “ 

In  order  to  test  the  effect  of  still  finer  crushing  Ore  A was 
passed  through  a 200  mesh  screen,  but  the  results  were  practi- 
cally the  same  as  with  150  mesh,  a trifle  lower  even. 

If.  however,  the  ore  is  crushed  so  as  to  pass  but  a 20  mesh 
screen  the  extraction  on  all  of  the  ores  tested  immediately  fell 
off  in  such  a manner  that  no  further  tests  were  made  on  such 
coarser  sizes.  The  results  of  these  tests  are  in  accordance  with 
the  practice  of  the  plants  of  the  Black  Hills,  as  will  be  seen  by 
referring  to  the  analyses  of  the  mill  products  of  several  plants  on 
the  preceding  pages.  The  product  of  rolls  and  screens  at  the 
Imperial  mill  is  very  close  to  that  of  a 30  mesh  laboratory  screen 
except  that  it  contains  a small  percentage  of  somewhat  coarser 
sands.  The  product  of  stamps  at  the  Dakota  mill,  Deadwood, 


•4 

contains  a somewhat  greater  percentage  of  fines,  (above  ioo 
mesh)  and  less  sands,  but  a considerable  percentage  of  the  sands 
is  coarser  than  40  mesh. 

In  the  product  from  the  Monadnock  Roller  mill  the  sands  are 
considerable  less  in  amount  than  in  the  product  of  the  30  mesh 
laboratory  screen  and  the  fines  considerably  more.  This  product 
is  probably  better  suited  for  extraction  than  the  stamp  battery 
product  above  mentioned.  In  general  it  is  true  that  while  indi- 
vidual blue  ores  will  differ  somewhat  in  the  fineness  of  crushing 
required,  material  that  is  coarser  than  30  to  40  mesh  (0.0195  to 
.01475  inches)  will  show  an  appreciable  decrease  in  extraction. 
Product  finer  than  40  mesh  (.01475  inches)  will  in  general  show 
but  little  better  extraction,  perhaps  2 to  3 per  cent,  than  40  mesh 
material.  It  seems,  therefore,  that  for  the  greater  portion  of  the 
denser  silicious  ores  very  fine  crushing  presents  no  advantage 
whatever,  but  that  efforts  directed  toward  keeping  practically  all 
of  the  sands  finer  than  30  mesh  and  preventing  excessive  sliming 
as  an  unnecessary  evil  is  what  is  called  for. 

Tests  that  have  been  made  on  sand  tailings  at  the  Dakota 
mill  show  practically  that  all  the  sizes  of  sands,  except  the  ones 
coarser  than  30  mesh,  have  the  same  value. 

THE  EFFECT  OF  BROMO  CYANOGEN  — The  effect 
of  bromo  cyanogen  while  not  what  was  hoped  for  is  still  very 
marked  on  all  of  the  blue  ores  treated  raw  as  the  following 
table  will  show: 


Ore. 

Percentage  of  Extraction. 

Plain  Cyanide. 

Percentage  of  Extraction. 
Cyanide  plus  Bromo  Cyanogen. 

Increase  in 
Extraction. 

( 54  per  cent 

J 63  per  cent 

( 7.0  per  ct 

A 

■J 

■j 

( 39  per  cent 

( 46  1 per  cent 

( 7.1  ; er  ct. 

B 

43  per  cent 

64  per  cent 

21.0 

C 

( 51  per  cent 

j 57*5  per  cent 

( 6.5  per  ct. 

( 50  per  cent 

l 57*5  Per  cent 

( 7.0  per  ct. 

The  effect  of  bromo  cyanogen  on  roasted  ore  is  not  so 
marked,  but  still  strong  in  evidence  as  the  following  table 
will  show: 


Ore. 

Percentage  of  Extraction  by  Roast- 
ing plus  Pla  n Cyanide. 

Percentage  of  Extraction 
Cyanide  plus  Bromo  Cyanogen. 

Increase  in 
Extraction  J 

j 75.5  : er  cent 

J 75.5  per  cent 

t no 

A 

1 80.7  per  cent 

I 85  8 per  cent 

1 5.1  per  ct. 

j 75.6  percent 

j 87.1  per  cent 

j n 5 per  ct 

1 82.0  per  cent 

) 82.0  per  cent 

| no 

B 

73.3  per  cent 

81.0  per  cent 

8 per  cent 

\ 63.5  per  c^nt 

1 69.5  per  cent 

( 6 per  ct. 

c 

•<  63.5  pei  cent 

-<  68.0  percent 

\ 4 5 Per  ct. 

( 5o  0 per  cent 

( 56.0  per  cent 

f 9.0  per  Ct. 

The  effect  of  bromo  cyanogen  on  the  siliceous  ores  of  the 
Black  Hills  is  to  act  merely  as  an  accelerator  in  the  solution  of 
the  gold  bearing  mineral  as  the  following  table  shows: 


Ore 

Percentage  ot  Extraction  by  Plain 
Cyanid'  , S days  contact  and  41  hours 
Agitation. 

Percentage  of  Extracts  11  ( , .ir.ide 
and  Bromo  C'  amgen,  36  to  4 hours 
A. nation. 

Perc  of  Ex 
Plain  Cy.  24 
36  hrs.  agi. 

A 

53  per  cent 

48  7 per  cent 

39  per  cent 

B 

7I  per  cent 

61. 4 per  cent 

43  per  cent 

The  effect  of  treating  the  raw  ores  for  a considerable  period 
with  a dilute  caustic  alkali  solution  before  cyaniding  has  a 
marked  effect  on  the  extraction  in  some  cases. 


Extraction  by  Plain  Cyanide 
With  ut  Alkali  Treatment. 

Extraction  by  Plain  Cyanide  and 
Alkali  Treatment. 

Ex. by  Cyanic' e plus 
bromo  cyanide  plus 

1 alkali  treat. 

A 

39  per  cent 

54  per  cent 

64  per  cent 

THE  EFFECT  OF  ROASTING. — The  effect  of  roasting 
on  the  ores  is  of  course  pronounced,  but  in  some  instances  does 
not  accomplish  by  any  means  what  might  be  expected  of  it. 
Some  of  the  ores  in  order  to  get  extraction  must  be  roasted 
with  great  care  as  regards  temperature.  The  temperature  must 
be  kept  low,  not  above  a very  dull  red  heat  for  3 to  4 hours, 
when  it  may  be  raised  to  decompose  any  sulphates  formed.  If 
the  temperature  be  raised  to  a bright  red  heat,  early  in  the " 
roasting,  with  some  ores , but  very  little  better  extraction  than 
on  raw  ore  can  be  obtained.  This  is  perhaps  due  to  the 
presence  of  small  amounts  of  arsenic  and  antimony  that  form 
stable  insoluble  compounds,  locking  up  the  gold  and  silver  vaU 


36 

ues.  The  effect  of  roasting  can  be  seen  from  the  following 
table: 


Ore 

Extraction  by  Plain  Cyanide,  Raw- 
Ore. 

Extraction  by  Plain  Cyanide,  roast- 
' edOre. 

1 ncrease  in 
Extracti  n. 

A 

. J 39  per  cent 

j 82  per  cent 

j 43  per  ct. 

) 33  per  cent 

1 75  per  cent 

1 42  per  ct. 

B 

) 47  per  cent 

j 76.6  1 er  cent 

j 29,6  per  ct 

1 40  per  cent 

1 73.3  per  cent 

I 33.3  per  ct 

O 

j 50  per  cent 

j 63.5  per  ct.* *  50  rer  ct.+ 

j 13.5  per  ct 

1 51  per  cent 

1 69.5  per  ct.*  56  per  ct.f 

) 18,5  per  ct 

With  ore  B,'  roasting  at  a low  heat  for  several  hours,  and 
then  mixing  with  charcoal  and  reroasting  was  tried,  but  with 
no  better  effect  than  before. 


TIME  REQUIRED  FOR  THE  EX  TRACI  ION  OF  THE 
VALUES . — Twenty-four  hours  continual  agitation  is  about  the 
minimum  limit  of  time  in  order  to  get  the  extraction  the 
ore  will  yield.  Below  that  extraction  will  suffer  materially.  In- 
creased time  of  agitation  36  to  48  hours,  gives  a somewhat  in- 
creased extraction,"  but  after  that  the  increase  of  time  gives  but 
little  increase  of  extraction,  although  of  course  a constant  incre- 
ment of  increase  is  noted,  * if  the  formation  of  soluble  sulphides 
be  avoided  by  the  addition  of  a soluble  lead  salt  or  zinc  sulphate 
in  small  quantities. 

GENERAL. — A chlorination  test  on  the  ore  B after  roast- 
ing was  made  and  gave  an  extraction  of  75.5  per  cent  as  com- 
pared to  81  per  cent  by  roastmg,  cyanide  and  bromo  cyanogen. 
Ore  B,  150  mesh  material,  was  also  treated  with  a solution  of 
aqua  regia  with  boiling  to  see  the  effect  and  an  extraction  of 
84.4  per  cent  was  made,  showing  the  exceeding  refractoriness  of 
a portion  of  the  values  in  this  class  of  ores. 

From  the  experience  gained  in  the  tests  made  it  seems  that 
a portion  of  the  values  of  the  blue  ores  are  practically  insoluble 
in  a cyanide  solution,  and  that  this  insoluble  compound  is  in 
many  instances  only  partially  altered  by  roasting. 

If  a portion  of  the  values  were  locked  up  in  the  gangue  of  the 
ore  so  that  it  could  not  be  extracted  for  this  reason,  it  would  seem 

* Roasted  at  low  heat. 

f “ at  once  at  a hi"h  heat. 

* See  also  Bulletin  No.  3 South  Dakota  School  of  Mines.  Cyanide  ex- 

periments, by  G.  H.  Clevenger  and  A.  Forsyth. 


37 


that  such  fine  crushing  as '200  mesh  would  certainly  liberate  the 
greater  part  of  it  and  thus  permit  a decided  increase  of  extrac- 
tion. But  this  is  not  so  as  can  be  plainly  seen  from  the  experi- 
ments. For  these  reasons  the  low  extraction  in  most  cases 
must  be  ascribed  the  non-solubility  of  a compound  containing 
a portion  of  the  values,  and  any  effort  toward  finer  crushing 
beyond  the  limits  specified  above,  or  a continued  contact  or 
leaching  for  a longtime  will  be  without  results.  However  the 
time  of  treatment  given  the  ores  is  a very  important  matter,  as 
it  must  be  continued  long  enough  to  be  well  above  the  mini- 
mum. There  is  also  some  evidence  that  when  the  time  of  treat” 
ment  is  continued  for  a considerable  period  of  time  that  soluble 
sulphides  tend  to  form  which  may  lower  the  extraction 
unless  some  zinc  be  present  in  the  solution  to  prevent  their 
presence  which,  however  fortunately,  is  usually  the  case  in 
ordinary  mill  solutions. 

METHOD  OF  APPLYING  THE  BROMO  CYANOGEN 
TO  THE  MILL  SCHEME  OF  THE  WET  CRUSHING 
PLANTS.  — This  is  largely  a matter  of  experiment,  but  the  first 
addition  might  take  place  just  before  the  solution  enters  the 
battery.  A 3 to  5 per  cent  bromo  cyanide  solution  could  be  in- 
troduced by  a small  pipe  into  the  battery  mains  and  regulated 
to  furnish  an  amount  of  bromo  cyanide  solution  so  that  the  bat- 
tery solution  would  contain,  say,  0.01  per  cent  to  0.02  per  cent 
of  bromo  cyanide.  If  added  in  this  place  the  agitation  given  by 
the  stamps  could  be  taken  advantage  of.  There  is  probably  one 
very  serious  objection  to  the  addition  of  bromo  cyanide  to  the 
mill  scheme  as  at  present  carried  out  and  that  is  the  alkalin- 
ity of  solutions  due  to  the  lime  added.  As  pointed  out,  alkalies 
destroy  bromo  cyanogen,  probably  without  the  formation  of  cy- 
anogen, and  it  is  very  likely  lhat  the  alkaline  earth  hydrates 
will  do  the  same.  It  may  be  possible  that  if  the  battery  solution 
entering  the  batteries  carries  but  very  little  protective  alkalinity 
and  the  amount  of  lime  added  with  the  ore  be  cut  down  as  low 
as  possible, something  might  still  be  accomplished  with  the  bromo 
cyanogen. 

This  is  a matter  of  experiment.  In  West  Australia  * at  Kal- 
goorlie,  lime  is  added  after  the  agitation  of  the  pulp  with  cyan- 
ide and  bromo  cyanogen  solution,  but  as  the  solutions  are  re- 


* The  Diehl  process,  by  H.  Knutzen,  Trans.  Ins.  M.  and  Met.  June  19, 
1902. 


38 

used  must  contain  some  lime  when  used  with  the  bromo  cyano- 
gen. 

The  next  place  where  an  addition  of  bromo  cyanide  can  be 
made  is  during  the  first  addition  of  barren  solution  to  the  slimes. 
It  could  be  added  in  amount  so  that  the  resultant  solution  in  the 
slimes  vat  will  contain  from  o.oi  to  0.02  percent  bromo  cyanogen. 
If  desirable  another  addition  of  bromo  cyanogen  solution  may 
be  made  at  a subsequent  addition  of  barren  solution. 

The  constant  addition  of  bromo  cyanogen  to  the  battery  so- 
lution would,  however,  require  considerable  bromo  cyanogen 
per  day  and  unless  a rather  marked  increase  of  extraction,  due 
to  its  addition,  could  be  noticed,  would  hardly  be  profitable. 

For  example,  in  a plant  crushing  125  tons  of  ore  per  day 
using  4 tons  of  a 2 pound  battery  solution,  per  ton  of  ore,  the 
amount  of  bromo  cyanogen  required  would  be  120  pounds,  in 
order  to  get  0.01  per  cent  of  bromo  cyanogen  in  the  battery. 
This  would  cost  $66  exclusive  of  an  increased  consumption  of 
potassium  cyanide  due  to  the  addition  of  bromo  cyanogen. 

On  $8  ore,  therefore,  in  order  to  make  the  addition  of  bromo 
cyanogen  profitable,  an  increase  of  at  least  7 per  cent  must  be 
shown  in  the  extraction,  due  to  the  addition  of  the  bromo  cyano- 
gen to  the  battery  alone.  The  question  would  have  to  be  worked 
out  on  a working  scale  in  the  mills  themselves,  and  the  cost  of 
the  experiment  would  not  be  very  great,  as  experiments  go. 


.39 


The  Crushing  in  Cyanide  Solution  Process  as  Carried  on 
in  ihe  Black  Hills  of  South  Dakota. 

by  Charles  H.  Fulton. 

INTRODUCTORY.—  The  crushingin  cyanide  solution  pro- 
cess was  first  introduced  into  the  Black  Hills  at  the  old  Dakota 
plant  at.  Central  City  by  Mr.  John  Hinton.  The  method  origin- 
ated in  New  Zealand,  being  first  used  by  F.  R.  -W.  Daw  in  1897, 
at  the  Crowns  mine.  In  the  Black  Hills  it  has  become  practi- 
cally the  established  method  for  the  denser  siliceous  ores,  there 
being  at  present  five  plants  in  operation  using  this  method,  with 
several  more  of  the  same  kind  projected.  The  dry  crushing 
process  still  holds  its  own  on  the  more  porous  and  open  sili- 
ceous ores  and  there  are  also  plants  in  operation  which  do 
fine  dry  crushing,  on  dense  siliceous  ores.  The  mills  em- 
ploying the  crushing  in  cyanide  solution  process  are  the  Horse- 
shoe mill,  120  stamps,  60  in  operation;  the  Dakota  mill,  30 
stamps;  the  Maitland  mill,  40  stamps;  the  Hidden  Fortune  mill, 
60  stamps,  and  the  Lundborg,  Dorr  & Wi’  on  mill,  a six  foot 
Monadnock  Roller  mill. 

THE  NATURE  OF  THE  ORES  TRY  A TED. — For  in- 
formation on  this  subject  reference  is  made  t } the  foregoing 
paper. 

GENERAL  TEA  TURES  OF  THE  PRQCESS. 

The  process  comprises  the  following  operations: 

1.  The  crushing  of  the  ores,  generally  by  stamps,  in  a 
cyanide  solution  ranging  from  1.3  to  2.2  pounds  of  cyanide  per 
ton,  and  carrying  a protective  alkalinity,  equivalent  to  1 to  1.5 
pounds  of  sodium  hydrate  per  ton. 

2.  The  separation  of  the  sands  from  the  slimes  by  means 
of  cone  classifiers. 

3.  The  treatment  of  the  sands  by  percolation. 

4.  The  treatment  of  the  slimes  by  agitation  and  decantation. 

5.  The  precipitation  of  the  values  by  means  of  zinc  thread. 

The  process  is  applicable  to  the  dense  siliceous  ores  that  re- 
quire a comparatively  fine  crushing,  and  which  contain  but  a 
small  quantity  of  cyanide  consuming  compounds.  For  ores  that 


40 


without  previous  alkaline  treatment  destroy  much  cyanide  the 
process  is  not  applicable.  As  a matter  of  fact  it  may  be  stated 
that  the  cyanide  consumption  in  this  method  is  higher  than  in 
dry  crushing.  The  cyanide  consumption  in  the  wet  crushing 
mills  of  the  district  varies  from  0.75  to  1.50  pounds  per  ton  of 
ore  treated.  At  a typical  dry  crushing  plant,  the  Imperial 
mill  at  Deadwood,  milling  the  same  class  of  ore,  the  consump- 
tion is  0.4  pound  per  ton.  At  the  other  dry  crushing  plants  of 
the  district  it  ranges  from  0.4  to  0.75  oound  per  ton.  The  in- 
creased consumption  of  cyanide  is  a defect  inherent  in  the  pro- 
cess for  several  reasons.  1.  Agitation  of  the  ore  with  cyanide 
solution  in  the  battery  causes  extra  consumption.  2.  Although 
the  battery  cyanide  solution  carries  a protective  alkalinity  (alka- 
linity above  that  due  to  cyanide  and  cyanogen  compounds)  of 
from  1 to  1.5  pounds  per  ton,  this  does  not  by  any  means  com- 
pletely protect  the  cyanide  from  destruction  by  cyanicides.  The 
reaction  between  cyanicides  and  cyanide  and  alkaline  earth  hy- 
drates and  caustic  alkalies  probably  takes  place  in  part  at  least 
simultaneously.  It  has  been  recognized  by  metallurgists  that  with 
many  ores  it  is  essential  to  apply  a comparatively  highly  alkaline 
solution  low  in  cyanide  to  the  ores  before  the  stronger  cyanide 
solutions  are  employed,  for  the  alkalinity  carried  in  the  strong 
cyanide  solution  would  be  ineffective  in  preventing  a considerable 
consumption.  3.  There  is  also  an  increase  in  the  consumption 
due  to  the  discharge' of  considerable  cyanide  in  the  moisture  go- 
ing out  with  the  slimes  tailings.  This  might  be  called  a mechan- 
ical consumption.  This  consumption  alone  amounts  to  from  0.3 
to  0.6  pounds  per  ton  of  ore  treated.  The  mechanical  consump- 
tion of  dry  crushing  plants  is  but  an  insignificant  factor. 

At  the  present  time  it  is  difficult  to  make  a comparison  as 
regards  the  relative  merits  of  the  process  under  discussion  and 
the  dry  crushing  process.  There  is  probably,  on  the  whole,  little 
difference  between  the  two  processes  as  regards  cost  although 
the  wet  crushing  mills  probably  have  a slight  advantage  in  this 
respect,  in  spite  of  the  slimes  treatment  and  the  higher  consump- 
tion of  chemicals.  The  wet  crushing  plants,  of  course,  have  an 
advantage  in  that  they  do  not  suffer  from  the  dust  nuisance. 
However,  the  hope  that  the  wet  crushing  plants,  on  account  of 
the  great  fineness  of  crushing  that  could  be  carried  on,  would  be 
able  to  treat  the  blue  ores  in  the  raw  state  successfully,  has  not 
been  verified  and  it  is  probable  that  for  this  class  of  ores  roast- 
ing will  finally  have  to  be  resorted  to.  In  this  case,  of  course, 


4i 


dry  crushing  will  have  all  the  advantage.  Some  of  the  mines  of 
the  district  furnish  but  little  blue  ore,  while  others  have  a great 
deal  in  their  reserves.  For  the  first  type  the  crushing  in  cyanide 
solution  method  is,  without  doubt,  a permanent  institution. 

THE  CRUSHING  OF  THE  ORES —The  ores  are  rough 
crushed  generally  by  Gates  crushers  and  in  one  instance,  at  the 
Maitland  mill,  by  a Blake  crusher.  The  crushed  ore  will  pass  a 
i.  5 to  2 inch  ring  and  is  fed  to  the  stamps  by  Challenge  feeds. 
Stamps  with  one  exception  are  used  for  the  fine  crushing  of  the 
ore.  The  Lundberg,  Dorr  & Wilson  mill  employs  a 6 foot 
Monadnock  roller  mill  fer  the  fine  crushing,  a set  of  rolls  being 
placed  between  the  Gates  crusher  and  the  roller  mill,  in  order  to 
get  the  proper  sized  feed  of  ore. 


The  following  table  gives  the  details  cf  the  stamps  at  four 
of  the  mills. 

Details  of  the  Stamp  Mills. 


Name  of  Mill 

Weight  of  Stain  . 

X 

o 

? 

T3 

</> 

gj 

5’ 

Height  of  Drop  Indies. 

Depth  of  Discharge,  In. 

sg 

i_.SI 

Ss- 

S O 

cr 

x 

2 cT 
a 3. 

r- 

< '33 
(t  0 
“ y,_ 

P 

Screen  Used 

Amount  of  Solution  per 
Ton  of  Ore. 

Capacity  per  Stamp  in 
tons  per  24  hrs. 

Type  of  Mortar. 

Hidden  Fortune* 

1 120 

9X 

' 7 

8 

16 

24  mesh.  *6  wire 

5 

4 

Double  issue 
rear  blocked  up. 

Maitland 

QIO 

97 

88 

7 to  8 

8 

6 

x3 

26  y 13  mesh 
26  wire. 

4 to  5. 

3-5t04 

Single  i sue. 

Dakota. 

950 

9 

*5 

10  by  4 mesh,  20 
w re. 

5 

r4 

Single  issue. 

Dakota 

950 

88 

8 : 

7 

22 

Same, 

5 

Double  issue 
rear  blocked  up. 

Horseshoe 

IOOO 

9o 

8 

5 to 

18 

i4  by  7 mesh,  21 
wire 

6 

4-5t°5 

Double  issue 
rear  blocked  up. 

*Crushing  in  very  dilute  cyanide  solution  and  amalgamating  with  inside  plate  and  over  tables. 


Some  of  the  earlier  mills  installed  double  issue  mortars  with 
the  idea  of  getting  an  increased  stamp  duty,  but  it  was  soon 
found  that  the  amount  of  solution  required  in  crushing  was  so 
great  that  the  mills  were  unable  to  handle  it  economically  and  the 
rear  discharges  were  closed  by  wooden  frames.  It  will  be  seen 
from  the  table  that  the  depth  of  issue  and  the  width  of  the  mor- 
tar at  the  discharge  level  vary  considerably  at  the  different  mills. 
The  weight  of  stamp  has  not  so  great  a variation. 

As  the  stamps  used  are  for  crushing  purposes  only  at  all  of 


42 


the  mills  with  the  exception  of  the  Hidden  Fortune,  it  would 
seem  that  in  general  a narrow  box,  a shallow  discharge  and  a 
heavy  stamp,  up  to  noo  to  1200  pounds  would  give  the  greatest 
capacity  and  most  economical  results.  However,  the  retaining 
of  the  ore  in  the  mortar  for  a certain  length  of  time  in  order  to 
agitate  thoroughly  with  cyanide  solution  is  desirable.  At  most 
of  the  mills  from  50  to  53  per  cent  of  the  values  of  the  ore  are 
extracted  in  the  batteries  and  the  classifying  cones.  Stamps  for 
this  type  of  crushing  should  attain  a capacity  of  5 tons  and  over 
per  stamp,  and  in  the  later  designs  of  mills  to  be  built  this  has 
been  provided  for.  At  some  of  the  mills  the  ore  is  very  hard 
which  in  part  accounts  for  the  rather  low  capacities. 

The  screens  used  also  vary  consider  ibly  at  the  different 
mills,  ranging  from  26  mesh,  26  wire,  to  10  mesh,  20  wire.  This 
is  necessitated  by  the  requirements  of  the  individual  ores  which, 
while  having  the  same  general  characteristics,  differ  somewhat 
in  the  fineness  of  crushing  required. 

Recently  several  of  the  mills  have  installed  wire  cloth  screens 
in  which  the  opening  is  rectangular,  instead  of  square,  tne  lo*:g 
dimension  in  these  screens  being  from  2 to  2.5  times  that  of  the 
short  dimension.  Screens  of  this  type  give  somewhat  greater 
capacity  and  do  not  choke  so  readily  as  screens  wnh  a square 
mesh. 

The  denser  siliceous  ores  require  a comparatively  fine  cruh- 
ing,  but  if  the  crushing  is  carried  beyond  a certain  fineness  noth- 
ing is  gained  in  extraction  and  trouble  is  encountered  in  the  pro- 
duction of  an  excessive  amount  of  slimes  which  are  difficult  to 
handle  in  the  mill.  It  has  been  demonstrated  that  if  the  ore  is 
crushed  so  that  the  great  bulk  of  it  is  not  co  imer  th  in  30  mesh 
(0.0195  inches)  and  not  finer  than  60  mesh,  (0.0075  inches,)  the 
economic  extraction  is  obtained.  Material  finer  than  60  mesh 
yields  but  v^ry  little  higher  extraction  than  that  between  30  and 
60  mesh. 

The  5 per  cent  greater  extraction  obtained  in  the  mills  on 
the  slimes,  although  the  recovery  is  the  same  as  on  the  sands, 
is  for  the  greater  part  due  to  the  agitation  obtained  in  the  treat- 
ment. If  the  size  of  the  ore  particles  however  is  coarser  than  30 
mesh  the  extraction  on  most  of  the  ores  is  materially  decreased. 

The  following  table  shows  the  nature  of  the  mill  product 
made  at  some  of  the  mills: 


Mechanical  Analyses  of  Mill  Products. 


t 


Name  of  Mill. 

Mesh  of  Screen 

Dakota  Samps. 
Screen  10  by  4 
mesh  20  wire. 

Lundborg,  Dorr 
& Wilson  Mon- 
adnock Roller 
Mill,  Screen  18 
Mesh,  0.046  i 
space 

Imperial, 

R 11s.  Screen  r6  mesh,  21 
wire. 

plus  20 

12,7  1 ercent. 

1.0  per  cent. 

3.0  per  cent. 

•xl 

plus  Mo 

18.0  { er  cent 

0 

n 

D 

rf 

plus  40 

22.0  pe"  cent. 

10  0 per  cent. 

17  0 1 er  c nt. 

'K 

n> 

0 

plus  60 

xo  0 per  cent. 

t6.o  per  cent. 

5 

(K 

; lus  80 

14.8  per  cent. 

5.0  per  cent. 

0 

cn 

plus  IOO 

6.0  per  cent. 

10.0  per  cen* . 

5.0  p r cent. 

3 

( * 

minus  too 

36.0  per  cent. 

plus  150 

14.8  per  cent. 

minus  150 

29.8  per  cent. 

plus  200 

19  0 per  cent. 

minus  200 

N 

50.0  per  cent. 

The  Dakota  mill  uses  the  coarsest  screens  of  any  of  the 
mills  and  gets  a product  about  20  per  cent  of  which  is  coarser 
than  30  mesh,  a rather  high  percentage,  but  in  view  of  the  very 
low  tenor  of  the  ores  treated,  and  their  shaly  nature,  this  crush- 
ing is  the  most  economic  that  could  be  practiced.  The  other 
mills  use  finer  screens  and  their  mill  product  approaches  closely 
to  that  of  the  Monadnock  mill  quoted  in  the  above  table.  One 
mill,  the  Hidden  Fortune,  crushes  some  cement  ore  which  con- 
tains a considerable  coarse  free  gold.  This  mill  has  adapted 
the  crushing  in  cyanide  solution  process  in  conjunction  with 
amalgamation  inside  and  outside  of  the  mortar.  A very  weak 
cyanide  solution,  1.5  pounds  per  ton,  is  used  with  success 
as  a battery  solution,  no  difficulty  being  experienced  to  get 
good  amalgamation.  The  plates  need  somewhat  more  frequent 
dressing  owing  to  the  hardening  action  of  the  cyanide  on  the 


44 

amalgam.*  It  is  also  very  probable  that  the  plates  will  have  to  | 
be  more  frequently  renewed  owing  to  the  solvent  action  of  the 
cyanide. 

WEARING  PARTS  OF  THE  STAMP  MILLS—  Most  of 
the  mills  have  adopted  chrome  steel  for  shoes  and  in  part  for  dies 
as  giving  the  most  satisfaction  and  being  the  most  economical. 
Table  III,  compares  the  different  materials  that  have  been  used. 

The  Cost  of  Shoes  and  Dies  of  Different  Material. 

Note . Shoes  weigh  180  pounds  and  dies  120  to  140  pounds. 
Laid  down  at  Terry,  S.  D.,  chrome  steel  costs  5.83c  per  pound,  | 
Wilson  forged  steel,  5.72c  per  pound,  and  cast  iron,  3.5c  per  j 
ponnd. 


Name  of  Mill. 

Name  of 
Part. 

Material 

Tons  of  Ore 
Crushed. 

No.of  Days 
Used. 

Cost  per  Ton 
of  Ore 

Cm  hed. 

Maitland 

Shoe 

Chrome  steel 

250 

90-95 

4.9c 

- 

Cast  iron 

105 

35-4  • 

4.05c 

“ 

Die 

Cast  iron 

105 

40 

3.28c 

“ 

Wilso.i  forged  steel 

280 

105 

3.06c 

Horseshoe 

Shoe 

Chrome  Steel 

336 

84 

3.I2C 

- 

“ 

Cast  iron 

104 

26 

6 15c 

“ 

“ 

Wilson  forged  steel 

280 

70 

3.67c 

“ 

Die 

Chrome  Stec-1 

400 

100 

2.29 

“ 

. .r.»  , 

120 

3o 

4 08 

Wilson  f.  rged  ste  1 

340 

85 

2.35 

The  Dakota  mill  also  uses  chrome  steel  shoes  and  is  experi- 
menting with  a cast  iron  die  containing  20  per  cent  of  chrome 
steel  scrap,  made  at  a local  foundry,  which  costs  3.5c  per  pound 
laid  down  at  the  mill.  Dies  of  this  kind  weigh  120  pounds  and 
lasted  46  days,  crushing  175  tons  of  ore  and  leave  14  pounds  of 
scrap  which  is  sold  at  0.5c  per  pound, 

At  the  Lundborg,  Dorr  and  Wilson  mill  at  Terry  a 6 foot 
Monadnock  roller  mill  is  used  to  crush  in  cyanide  solution  in 

* This  same  method  is  used,  in  part  at  one  or  two  mills  employing  the 
Diehl  Process  at  Kalgoorlie,  Australia.  See  the  Diehl  Process,  H. 
Knutzen,  Trans.  I.  M.  and  M.  June  1902, 


t 


•: 


Mortar  Box  for  Crushing  in  Cyanide  Solution. 


45 

place  of  stamps.  This  mill  crushes  about  70  to  90  tons  of  ore 
per  da}',  from  0.75  inch  size  through  an  18  mesh  screen,  0.046 
inch  space.  The  mill  makes  32  revolutions  per  minute  and  has 
19.5  square  feet  of  screen  area.  A peculiar  feature  in  the  wear 
of  this  mill  is  that  both  the  die  ring  and  the  roller  tire  cup  on 
bearing,  instead  of  the  die  cupping  and  tire  crowning.  This 
however  does  not  seem  to  affect  the  efficiency  of  the  crushing. 
The  mill  is  giving  satisfaction  but  no  figures  are  as  yet  available 
to  afford  a comparison  between  it  and  the  stamps  on  siliceous 
ore.  It  might  be  stated  that  the  ores  crushed  at  this  mill  are  in 
part  comparatively  soft  although  some  hard  blue  quartzite  ores 
are  also  being  crushed. 

The  cyanide  solution  is  introduced  into  the  batteries  at  most 
of  the  mills,  by  two  1.5  inch  pipes  entering  at  the  front  of  the 
battery  between  the  first  and  second  and  the  third  and  fourth 
stamps.  Each  pipe  is  controlled  by  an  iron  cock. 

At  two  of  the  mills  a special  form  of  mortar  is  used  having  a 
cast  iron  collecting  launder  bolted  on  at  the  front,  and  having  a 
central  discharge  into  the  main  launder  collecting  the  sludge  from 
all  the  batteries.  This  mortar  is  shown  in  the  accompanying  plate 
which  also  gives  the  form  and  dimensions  of  the  mortar  used  at 
the  Maitland  mill.  Generally  all  the  screens  are  overhung  with 
heavy  canvas  to  avoid  splash. 

THE  SEPARATION  OF  THE  SANDS  FROM  1HE 
SLIMES  BY  MEANS  OF  CONE  CLASSIFIERS  — 

This  is  no  v don?  in  the  district  almost  entirely  by  means  of 
simple  sheet  iron  cones.  These  cones  are  the  outer  cones  of  or- 
dinary hydraulic  classifiers,  the  inner  cones  having  been  re- 
moved. It  may  be  stated  at  the  outset  that  the  problem  of  re- 
moving the  sands  from  the  slimes  when  crushing  in  cyanide  so- 
lution with  considerable  lime  is  a more  difficult  problem  than 
when  crushing  in  water  with  practically  no  lime.  The  lime 
causes  much  trouble,  first,  by  its  coagulating  effect  on  the 
slimes,  causing  them  to  settle  with  , the  sands  and  coat  sand  par- 
ticles with  slimes,  and  second,  by  causing  the  formation  of  an 
excessive  amount  of  froth  or  foam,  which  is  certainly  a 
great  nuisance  about  the  mill.  The  plate  accompanying  this 
part  of  the  paper  shows  the  general  arrangement  of  the  classsi- 
fying  cones. 

The  batteries  discharge  their  sludge  by  launder  into  a cen- 
tral sump  from  which  it  is  raised  to  the  cones.  The  raising 


46 

pump  at  three  of  the  mills  is  the  Frenier  Spiral  sand  pump, 
and  at  one  of  the  mills  a centrifugal  pump.  For  the  raising  of 
the  battery  sludge  consisting  of  sands  and  slimes  the  Frenier 
pump  is  preferred  to  a centrifugal  on  account  of  less  wear. 
For  the  transference  of  slimes  and  for  their  agitation  a centrif- 
ugal pump  is  generally  used.  The  usual  size  of  the  spiral  sand 
pump  employed  is  the  54  by  10  inches.  These  pumps  are 
run  at  19  to  20  revolutions  per  minute,  raising  the  pulp  15  to  20 
feet.  Twenty  feet  is  about  the  practical  maximum  lift  of  these 
pumps  and  for  greater  lifts  they  are  placed  in  tandem.  A pump 
of  the  above  size  will  readily  handle  from  350  to  450  tons  of 
sludge  per  day. 

The  discharge  of  these  sand  pumps  is  intermittent  so  that 
at  all  of  the  mills  a distributor  box  is  used  to  steady  the  flow 
and  give  a uniform  feed  to  the'  cones.  These  distributing 
boxes  have  different  forms  at  the  various  mills.  At  the 
Horseshoe  mill  a pyramidal  box  is  used  4 by  4 feet 
in  cross  section  at  the  top,  the  sides  sloping  at  60 
degrees  to  meet  at  a point.  The  inverted  pyramid  is  topped 
by  a box  12  inches  high  through  which  the  two  4 inch  pipes  from 
the  sand  pumps  enter.  About  12  inches  from  the  bottom  of  the 
pyramid  four  three  inch  pipes  emerge  one  at  each  side,  which 
feed  into  four  50  inch  cones.  The  distributor  is  placed  centrally 
over  the  four  cones  and  as  low  as  possible  so  that  the  head  under  <x 
which  the  discharge  takes  place  will  be  small.  A screen  placed 
in  the  distributor  box  serves  to  keep  out  foreign  matter  from  the 
cones.  At  the  Maitland  mill  a plate  steel  box  6 by  3 feet  in 
cross  section  and  3 feet  deep  is  used  as  a distributor.  On  one 
side  2 1 inches  from  the  top  two  5 kich  pipes  enter  from  the  sand 
pumps  and  discharge  upon  an  inclined  screen.  The  two  discharge 
pipes  5 inches  in  diameter  which  feed  the  two  50  inch  cones  have 
their  centers  placed  4 inches  above  the  bottom  of  the  distri- 
butor box.  As  at  the  Horseshoe  mill  the  distributor  is  set  as 
closely  as  possible  to  the  cones.  At  the  Dakota  mill  a simitar 
box  made  of  wood  is  used. 

The  upper  cones  are  simple  cones  of  fsheet  iron  from  40 
to  50  inches  in  diameter  having  vertical  sides  at  the  top  12 
inches  high.  The  slope  of  the  cones  is  60  degrees  ending  in  a 
six  inch  sorting  column,  which  has  a two  inch  discharge  con- 
trolled by  an  iron  cock.  The  charging  pipe  feeds  at  the  cen- 
ter of  the  cone  just  below  the  pulp  level.  In  most  of  the  mills 
the  top  cones  are  covered  closely  by  either  a wood  or  an  iron 


■ 


Apparatus  for  the  Separation  ofuSlimes  from  Sands. 


, 47 

cover  to  confine  the  foam.  1 his  has  the  disadvantage,  not  very 
serious,  of  preventing  ready  inspection  of  the  cones. 

The  upper  cones  are  practically  simple  settling  cones.  The 
sludge  going  to  the  cones  contains  from  14  to  19  per  cent  of  sol- 
ids of  which  30  to  50  per  cent  is  slimes  and  the  rest  sands.  Just 
what  constitutes  sands  and  slimes  is  somewhat  difficult  to  de- 
fine.* It  is  rather  generally  accepted  by  the  men  in  charge 
of  the  plants,  crushing  siliceous  ores,  that  material  finer  than 
150  mesh  is  a slime  and  coarser  than  150  mesh  a sand,  and 
I classification  is  made  largely  on  this  basis;  It  has  also  been  de- 
fined as  that  portion  of  the  crushed  ore  that  will  make  water 
1 muddy,  sands,  no  matter  how  fine,  settling  practically  at  once 
and  not  remaining  suspended.! 

The  overflow  from  the  upper  cones  contains  practically  no 
sands,  even  very  line,  and  goes  to  the  slimes  tanks  by  the  overflow 
launder.  The  sands  discharged  at  the  bottom  of  the  cones  con- 
tain from  20  to  35  per  cent  of  slimes  anc  are  distributed  by 
a short  box  to  the  lower  cones.  These  lowe^  cones  are  of  the 
same  construction  as  the  upper  ones,  but  have  introduced  into 
the  sorting  column  an  upward  current  of  cyanide  solution  either 
battery  solution  or  barren  solution  (solution  that  has  been  pre- 
cipitated), but  generally  battery  solution.  This  solution  is  in- 
troduced through  a 2 inch  pipe  with  a cock  to  regulate  the  flow. 
The  amount  of  solution  introduced  in  this  way  amounts  to  from 
60  to  8o  tons  per  24  hours  for  a 42  to  50  inch  cone.  These  figures 
vary  sgmewhat,  those  given  representing  the  limits.  The  num- 
ber of  lower  cones  is  always  one-half  that  of  the  upper  cones.  The 
solution  pipes  entering  the  sorting  column  of  the  lower  cones  do 
not  come  directly  from  the  stock  tanks,  but  from  a special  box 
provided  with  an  overflow  at  a definite  height,  so  that  the  .head 
1 of  the  entering  solution  is  always  constant. 

The  final  sand  discharge  containing  25  to  30  per  cent  solids, 
aind  containing  from  1 to  5 per  cent  of  slimes,  goes  to  the  But- 
ters distributors  over  the  sand  vats,  battery  solution  being 
added  in  the  carrying  launder  so  as  to  have  5 parts  of  solu- 
1 tion  to  1 part  of  sand.  The  mills  endeavor  to  make  a fairly 
close  separation  of  sands  from  slimes  in  order  to  get  a good 
leaching  rate  in  the  sand  tanks,  usually  from  2.5  to  3.5  inches 

*What  constitutes  a slime?  W.  J.  Sharvvood,  E.  & M.  jour.  vol.  76, 
p.  539,  650. 

■{■Thus  defined  by  Mr.  John  Gross,  in  a paper  read  before  the  Black 
Hills  Mining  Men’s  Ass.  “Cyanide  Practice  at  the  Maitland  Prop- 


48 

per  hour,  although  at  one  plant  it  is  but  1.5  to  1.75  inches  per 
hour  and  also  to  prevent  trouble  which  the  sands  give  in  the 
slimes  tanks,  that  of  settling  to  the  bottom  and  remaining  there 
during  the  greater  part  of  the  treatment  practically  unacted 
upon.. 

A very  close  and  satisfactory  separation  however  is  not  pos- 
sible, first  on  account  of  the  inherent  defects  of  the  cones  used  as 
classifiers  and  second  because  of  the  bad  effect  of  the  lime  in 
sending  slimes  with  the  sands  as  already  mentioned.  For  these 
reasons  the  classification  adopted  is  that  of  making  a clean  sand 
rather  than  a clean  slime,  this  being  the  lesser  of  two  evils.  For 
example  at  the  Maitland  mill  the  sands  carry  only  one  to  two 
per  cent  of  slimes,  five  percent  giving  an  unsatisfactory  leaching 
rate.  In  making  sands  of  this  kind  the  slimes  run  from  15  to  20 
per  cent  of  fine  sands,  but  a small  portion  of  which  remains  on  a 
1 50  mesh  screen.  The  proportion  of  the  ore  crushed  treated  as 
sands  and  slimes  varies  at  the  different  mills.  At  the  Maitland 
mill  the  average  figures  for '8  months  show  48.2  per  cent  of 
the  ore  treated  as  sands  and  51.8  per  cent  treated  as  slimes.  At 
the  Dakota  mill  the  sands  amount  to  65  to  70  per  cent  and  the 
slimes  to  30  to  35  per  cent.  At  the  Lundorg,  Dorr  and  Wilson 
mill  the  sands  and  slimes  amount  to  approximately  50  per  cent 
in  each  case.  At  the  Horseshoe  mill  the  slimes  amount  to  26  to 
30  per  cent  and  the  sands  to  70  to  74  per  cent. 

A number  of  different  systems  of  classification  by  the  cones 
were  tried  before  the  system  described  was  adopted.  It  will  be 
noticed  that  the  system  now  used  reclassifies  the  sands  from  the 
upper  cones.  Formerly  the  plan  was  to  reclassify  the  slimes 
overflow  from  the  upper  cones  in  the  lower  cones,  but  this  prac- 
tice was  soon  discarded  as  unsatisfactory,  giving  in  some  in- 
stances unleachable  sands.  Double  cones  were  also  used,  i.  e.- 
the  regulation  cone  classifier,  but  most  of  the  mills  now  classify 
with  the  inner  cone  removed.  The  only  mill  where  a double 
cone  with  an  upward  current  is  used  to  reclassify  the  sands  is  at 
the  Hidden  Fortune  mill. 

Two  of  the  mills,  the  Lundborg.  Dorr  & Wilson  and  the 
Hidden  Fortune,  unwater  the  slimes  before  they  go  to  the  slimes 
tanks  The  first  by  means  of  a large  sheet  iron  cone  22  feet 
in  diameter,  the  top  portion  sloping  40  degrees  and  the  lower 
portion  near  the  discharge  60  degrees,  and  the  second  by  means 
of  a 3 compartment  spitzkasten  40  feet  long,  6 feet  wide  and 
8 feet  deep.  The  compartments  are  charged  successively  and 


49 

the  thickened  slimes  drawn  off  and  mixed  with  solution  in  the 
launder  that  transfers  them  to  the  slimes  tanks.  The  object  of 
un watering  the  slimes  in  this  way  is  to  give  them  an  additional 
treatment  with . barren  solution,  for  when  not  unwatering  the 
slimes  they  go  to  the  slimes  vat  with  battery  solution  and  are  set- 
tled there  for  the  first  time,  while  with  the  unwatering  device  the 
slimes  go  to  the  slimes  tanks  with  barren  solution  having  had  one 
dilution  by  the  time  they  reach  the  first  slimes  tank.  The  scheme 
of  classification  at  the  Hidden  Fortune  mill  is  given  below  as  it 
is  somewhat  different  from  that  of  the  other  mills: 

Stamp  Batteries  (60  stamps,) 


Amalgamated  Plates 


i 

2 72  inch  Cones  (simple  settling  cones,) 


Slimes  overflow 


Sands 


3 Compartment  Spitzkasten  Settler. 


Solution  to  Thickened  Slimes 

sand  vats 

1 

To  Slimes  Vats  with 
barren  solution. 


2 50  inch,  double  cones 
with  upward  current  of 
solution. 


overflow  Sands 

~r  r 

| To  Butters 

distributors 


1 50  inch  simple 
cone  with  upward 
current  of  solution  To  Sand 


/ \ Vats. 

/ \ 

overflow  fine  sands 

to  Spitzkasten 

Settler.  to  the  Butters 

Distributors. 


To  show  the  nature  of  the  classification  at  some  of  the  mills 
the  following  mechanical  analyses  of  sands  and  slimes  is  ap- 
pended: 


50 

MECHANICAL  ANALYSES  OF  SANDS  AND  SLIMES. 


Sands  at  the  Dakota  mill  constitut- 
ing 70  per  cent  of  the  mill  product 

Slimes  at  the  Dakota  mill  constituting 

30  per  cent  of  the  mill  product. 

On  a 20  mesh  screen  13  to  20  per  cent. 
““40  “ “ 30  “ “ 

“ “ 80  “ “ 26“  54  “ “ 

“ “ 100  “ “ 7 t;  8 “ “ 

■"  “150  “ ‘ 13  “ 18  “ “ • 1 

Passed  a 150  mesh  4**5  “ “ 

On  a 100  mesh  scre’n  0.3  to  0.4  per  ct. 

On  a 150  mesh  screen  12  to  33  percen 
Passed  a 150  mesh.  60  to  87  ‘ *' 

Sands  at  the  Lundborg,  Dorr*  and 
Wilson  mill,  constituting  50  per  cent 
of  the  mill  product. 

I Slimes  at  the  same  mill,  constituting 

50  per  cent  of  the  mill  product. 

On  a 40  mesh  screen  30  per  cent. 

“ “ 100  “ “ 40  “ 

“ “ 200  “ “ 24  “ “ 

Passed  a 200  mesh  6 “ “ 

On  a 60  mesh  screen 0.5  percent. 

“ 100  “ ‘ 1.5  “ 

“ ‘ ' 200  “ “ 18  “ 

, Passed  a 200  mesh  scr  fn8o‘-  “ 

It  may  be  noted  that  a comparison  of  these  products  at 
the  different  mills  is  not  possible  as  the  ores  differ  and  what  is  a 
fine  sand  at  one  mill  according  to  mesh  size  may  be  a slime  at 
another. 

The  proper  separation  of  the  sands  from  the  slimes  is  a 
vital  question  to  be  solved  with  the  plants  of  the  Black  Hills  and 
is  one  that  has  given  the  mill  men  much  trouble.  While  the 
present  system  is  a great  improvement  on  the  uractice  of  the 
earlier  mills  there  is  still  much  room  for  further  improvement. 

THE  TREATMENT  OF  THE  SANDS.— The  filling  of 
the  sand  tanks  is  accomplished  by  distributors  of  the  Butters  and 
and  Mein  type,  the  construction  of  which  is  shown  in  some 
detail  in  the  accompanying  plate.  The.  distributor  is  sus- 
pended from  a trolley  running  on  tracks  above  the  sand  vats,  so 
that  the  distributor  can  readily  be  transferred  from  one  vat  to 
the  other.  The  sands  are  fed  into  the  hopper  of  the  distributor  by  a 
launder,  which  feeds  as  near  the  center  of  the  hopper  as  possible, 
avoiding  the  throwing  of  the  feed  against  the  sides  as  this  causes 
an  irregular  distribution  of  the  sands  in  the  vat.  The  dimen- 
sions of  the  distributors  vary  according  to  the  capacity  required. 
The  slope  of  the  pipe  arms  is  i in  12,  and  the  diameter  of  the 
pipes  varies  in  the  different  distributors  from  1.5  to  2.5  inches. 
Generally  all  the  pipe  arms  in  a distributor  are  of  the  same  di- 
ameter, but  in  the  one  at  the  Horseshoe  mill  the  long  arms  are 
3.5  inches,  the  medium  arms  are  2.  5 to  3 inches  and  the  short 
arms  2 inches  in  diameter.  The  discharge  nozzles  are  usually 
separate  castings,  the  discharge  being  controlled  by  wooden 

* This  mill  has  replaced  cone  classifiers,  by  a mechanical  classifier,  the 

invention  of  Mr.  J.  V.  N.  Dorr. 


Distributor  for  Sands. 


5i 

plugs.  The  number  of  arms  is  generally  six,  although  the  distribu- 
tor at  the  Horseshoe  mill  has  8 arms.  In  the  case  of  one  of 
the  six  arm  distributors  the  following  figures  give  the  length  of 
arms.  13.25  feet,  11.5  feet,  9.5  feet,  8.0  feet,  5.5  feet  and  2.5 
feet.  These  arms  are  unsymmetrically  hung  in  such  a 
way  that  their  weight  balances  the  distributor.  The  dis- 
charge of  the  pipe  arms'  must  cover  the  surface  of  the 
vat.  The  hoppers  of  the  distributors  are  provided  with  a hori- 
zontal screen  to  keep  foreign  mai-ter  out  of  the  pipe  arms.  The 
function  of  the  distributors  in  the  mills  crushing  siliceous  ore  is 
not  in  part  that  of  a classifier  acting  with  a filled  vat  in  removing 
slimes  from  sands,  but  it  acts  solely  to  evenly  distribute  sand  in 
the  vats.  The  sands  are  not  laid  down  under  \vater  or  solution, 
but  the  vat  is  what  might  be  called  dry  filled,  the  solution  which 
goes  into  the  vats  continually  draining  off  through  the  filter  un- 
til the  vat  is  full  of  sands.  The  top  layer  of  sands  in  the  vat  is 
always  practically  dry.  This  method  of  filling  has  the  advantage, 
first,  that  the  slimes  in  the  pulp  are  uniformly  distributed  with 
the  sands  in  the  vat,  which  is  not  the  cnse  when  direct  filling  is 
employed  under  water;  second,  that  for  this  reason  it  gives  a 
charge  that  is  more  percolable,  and  third,  that  during  the  fill- 
ing a great  amount  of  solution  passes  through  the  sands,  in  this 
way  treatment  going  on  all  the  time  that  the  vat  is  filling.  The 
charge  laid  down  in  this  way  is  also  more  porous  than  when 
laid  down  under  water.  At  the  Maitland  mill  the  amount  of  so- 
lution passing  through  a 1 50  ton  charge  of  sands  while  filling  is 
700  tons,  or  4.7  tons  of  solution  per  ton  of  sands. 

The  time  of  filling  a 30  by  6 foot  vat  at  the  Maitland  mill  is 
60  hours;  at  the  Lundborg,  Dorr  & Wilson  mill  a vat,  18  by  10 
feet  is  filled  in  60  to  72  hours.  At  the  Dakota  mill  a 115  ton  vat 
is  filled  in  38  hours. 

The  method  of  filling  formerly  employed  at  the  first  wet 
crushing  plants  of  the  Hills,  the  Portland  and  the  Dakota 
Mills,  was  the  indirect  method,  settling  boxes  with  two  com- 
partments being  used,  these  compartments  alternately  discharg- 
ing their  contents  into  the  sand  vats  below,  where  the  charges 
were  raked  over  and  leveled  off.  At  the  Dakota  mill  double 
treatment  of  the  sands  was  also  resorted  to,  but  discarded  as  un- 
necessary after  a year’s  trial.  The  settling  boxes  were  found  to 
be  such  inefficient  classifiers  that  the  cone  system  described  was 
evolved  and  the  sands  charged  at  some  of  the  mills,  by  distribu- 
tors into  the  sand  vats  filled  with  solution.  All  of  the  plants  how- 
ever soon  adopted  the  method  of  “dry  filling”  described  as 


52 


more  satisfactory. 

The  general  method  of  the  treatment  of  the  sands  is  the  same 
at  all  of  the  mills  although  the  amount  of  solutions  and  the  time 
of  treatment  varies.  The  treatment  of  the  sands  is  determined 
as  far  as  extraction  will  permit  the  problem  of  handling  the 
mill  solutions,  which  in  a plant  of  the  type  under  discussion  is 
quite  complex  as  might  be  expected. 

The  following  table  shows  some  of  the  details  of  sand  treat- 
ment: 


Name  of  Mill. 

Capacity  - of 

Tank. 

• 

Amount  of 
solution  pas- 
sing while 
filling. 

Amount  of  | Amount  of 
Battery  1 Barren 
Solution.  Solution. 

Amount  of 
Wash  Water 

Total  Time. 
Days. 

Maitland 

1 40  tons 

700  tons 

900  tons  450  tons 

15  tons 

16 

Dakota 

X15  tons 

86  tons 

63  tons 

I 

20  tons 

5 

Horseshoe 

350  tons 

4oo  tons 

• 

8 

Solutions  are  leaching  through  the  sands  continually,  there 
being  no  “contact”  or  solution  standing  on  the  ore  as  in  dry 
crushing  mills.  There  is  also  no  strong  solution  properly 
so  called,  although  the  battery  solution  and  the  barren  solu- 
tion differ  slightly  in  strength,  in  some  mills  the  barren  solution 
being  the  stronger  while  in  others  the  battery  solution  is  the 
stronger.  At  the  Maitland  mill  the  battery  solution  carries  1.20 
to  1.30  pounds  of  cyanide  per  ton,  and  the  barren  solution  1.50 
to  1.60  pounds  per  ton.  At  the  Horseshoe  mill  the  battery  so- 
lution carries  1.4  pound  of  cyanide  per  ton  and  the  barren  so- 
lution is  somewhat  stronger,  though  of  indefinite  strength.  At 
the  Horseshoe  mill,  the  overflow  solution  from  the  slimes 
vats  while  these  are  filling,  is  standardized  in  a sump  tank 
up  to  three  to  four  pounds  of  cyanide  and  then  run  through 
the  sands.  At  the  Dakota  mill  the  battery  solution  con- 
tains 2.2  pounds  of  cyanide  per  ton,  and  the  barren  solution 
two  pounds  per  ton.  At  the  Lundborg,  Dorr  & Wilson  mill 
the  battery  solution  contains  two  pounds  of  cyanide  per  ton 
and  at  the  Hidden  Fortune  mill  it  contains  1.3  pounds 
per  ton.  The  amount  of  wash  water  varies  but  little  at 
the  different  mills  amounting  to  o.  1 to  0.2  tons  per  ton  of 
sand.  Little  wash  water  is  required  as  the  cyanide  solutions  are 
all  weak  and  such  large  amounts  of  solution  are  passed  through 
the  sands  in  most  of  the  mills.  The  deficit  of  solutions  in  the 


Sand  Vats,  Mogul  Mill,  Horseshoe  Mining  Company. 


53 

mills  is  made  up  mainly  from  wash  water  added  in  the  slimes 
treatment. 

The  following  figures  show  the  result  on  sands  obtained  at 
the  Dakota  mill,  over  a period  of  5.50  months:  The  average 
value  of  the  ore  was  $4.75  per  ton.  The  sand  tailings  averaged 
§1.22  per  ton.  This  gives  an  extraction  of  74.25  per  cent  on  the 
sands.  The  moisture  going  out  with  the  sand  tailings  had  a 
value  of  40  cents  per  ton.  During  May,  1904,  the  average  value 
of  the  ore  was  $4. 55  per  ton.  The  average  value  of  the  sand 
heads  as  charged  into  the  vats  was  $2.60  per  ton,  the  average 
value  of  the  sand  tails  unwashed  was  $1.06  per  ton  giving  an  ex- 
traction of  76.7  per  cent  on  the  sands.  Comparing  the  original 
value  of  the  ore,  the  sand  heads  and  the  sand  tails,  it  is  evident 
that  42.8  per  cent  of  the  extraction  takes  place  in  the  batteries 
and  cones,  and  33.9  per  cent  during  the  sand  treatment  proper.' 

At  the  Hidden  Fortune  mill  the  extraction  on  the  sands 
averages  75  per  cent.  For  the  extraction  on  the  slimes  and  the 
total  extraction  reference  is  made  to  the  figures  given  under 
slimes  treatment. 

THE  TREATMENT  OF  THE  SLIMES  BY  AGITA- 
TION AND  DECANTATION . — There  are  two  systems  of 
slimes  treatment  practiced  in  the  Hills. 

1.  That  in  which  the  treatment  of  the  slimes  is  completed 
in  the  vat  into  which  they  are  originally  charged,  and  in  which 
most  of  the  agitation  is  performed  by  compressed  air. 

2.  That  in  which  the  slimes  are  successively  transferred 
from  one  vat  to  another,,  there  being  generally  three  to  four 
transfers  before  the  slimes  are  discharged.  The  agitation  in 
this  case  is  done  by  means  of  centrifugal  pumps. 

The  first  method  is  practiced  at  the  Horseshoe  mill  as  fol- 
lows: there  are  16  slimes  tanks,  14  feet  in  diameter  and  10 
feet  deep  and  two  30  feet  diameter  and  16  feet  deep.  The  ar- 
rangement of  a slimes  tank  as  shown  in  the  accompanying  plate. 
A partition  curtain  runs  down  to  nearly  the  bottom  at  one  side 
of  the  tank  behind  which  the  slimes  are  charged  as  they  come 
from  the  cones.  Before  charging  slimes  the  vat  is  filled  with 
barren  solution,  then  the  slimes  are  run  in,  the  surplus  solution 
running  off  clear  at  the  lip,  any  foam  being  held  back  by  a 
strip  of  wood  or  lath  resting  on  the  surface  of  the  solution.  Four 
to  six  pounds  of  lime  are  added  per  ton  of  ore  at  the  batteries 
for  the  coagulation  of  the  slimes,  this  being  the  only  addition  of 
lime  made  in  the  mill.  The  addition  of  lime  must  be  some- 


54 

what  nicely  adjusted  as  too  little  lime  f tils  to  coagulate  the 
slimes  readily  and  too  much  gives  trouble  in  the  precipitation  of 
the  values  later  on.  The  slimes  settle  rapidly  and  the  solution 
usually  runs  off  clear  at  the  lip  until  the  slimes  have  accumu- 
lated to  the  extent  of  about  50  inches,  equivalent  to  about  25  to 
30  tons  of  dry  slimes.  When  ihe  solution  at  the  lip  becomes 
cloudy  the  slimes  charge  is  turned  into  the  next  tank  and  the 
slimes  in  the  tank  just  filled  are  permitted  to  settle.  This  set- 
tling takes  about  ten  hours.  While  the  slimes  are  settling  the 
supernatent  solution  is  decanted  off  by  means  of  a decanting 
device  which  is  a simple  wooden  frame  with  a pipe  at  the  cen- 
ter which  is  connected  with  a take-off  pipe  about  18  inches 
from  the  bottom  of  the  vat.  (See  plate.)  It  is  important  to 
permit  the  slimes  to  settle  as  lovv  as  they  possibly  can  and  to 
cecant  as  closely  as  possible  without  taking  any  of  the  muddy 
solution.  The  object  of  the  slimes  treatment  in  the  main  is  to 
remove  by  successive  dilutions  the  dissolved  values,  so  that  it  is 
evident,  unless  the  decantation  is  as  close  as  possible  each  time, 
it  partly  fails  in  its  object.  The  solution  can  usually  be  de- 
canted within  an  inch  of  the  settled  slimes.  When  the  de- 
cantation is  complete  a wash  of  barren  solution  is  added, 
amounting  generally  to  40  tons  and  during  the  addition  of  this 
the  charge  is  agitated  by  compressed  air  at  40  pounds  pressure 
per  square  inch.  The  air  is  intrdouced  on  the  bottom  of  the  vat 
through  two  S shaoed  pipes  crossing  each  other,  and  having 
o.  12  inch  perforations.  The  only  agitation  the  slimes  receive  is 
that  obtained  by  the  air.  The  agitatiqn  by  air  alone  is  a weak 
point  in  that  it  fails  to  move  all  of  the  material,  especially  the 
heavier  portion  of  the  slimes  and  the  fine  sands  at  the  bottom  of 
the  vat.  For  that  reason  on  discharging  a vat,  it  is  not  sluiced 
out,  but  what  slimes  will  run  out  by  the.  bottom  gates  are  let  go, 
and  the  heavy  thick  slimes  remaining,  amounting  to  twoTo  four 
tons  per  charge,  form  again  a portion  of  the  next  charge  thus  get- 
ting two  treatments.  Each  charge  of  slimes  gets  four  to  six 
washes  with  barren  solution  and  one  wash  with  water,  each 
wash  amounting  to  40  tons.  This  gives  6.5  tons  of  barren  solu- 
tion and  1 to  1.6  tons  of  wash  water  for  each  ton  of  dry  slimes 

treated. 

The  slimes  as  discharged  contain  very  close  to  50  per  cent 
moisture.  From  ore  averaging  $8  to  $9  per  ton  dried  slimes 
tailings  average  $1.75  per  ton,  30  to  40  per  cent  of  which  still 
existed  as  gold  in  solution.  This  gives  the  washed  slimes  tail- 


i 


Slimes  Vat  and  Accessories. 


55 

iligs  a value  of  $1.24  per  ton  and  the  solution  discharged  as 
moisture,  a value  of  50  cents  per  ton. 

In  the  treatment  of  slimes  by  successive  dilutions  for  the  ex- 
traction of  the  values  where,  in  the  total  treatment  a definite 
amount  of  solution  is  used  per  ton  of  dry  slimes,  it  is  theoretic- 
ally required,  in  order  to  get  the  maxim  extraction,  to  use  the 
amount  of  solution  in  a comparatively  large  number  of  dilutions 
of  small  amount  each  time,  rather  than  a few  dilutions  of  large 
amount  each  time.  Thus,  in  treating  a ton  of  slimes  with  six 
tons  of  solution,  it  is  theoretically  better  to  give  six  dilutions  of 
one  ton  each,  rather  than  two  dilutions  of  three  tons  each.  If 
any  one  dilution  is  larger  than  the  other  it  should,  of  course,  be 
applied  when  the  silines  are  highest  in  value.  It  must  be  borne 
in  mind  however,  that  in  the  slimes  treatment  there  is  a solu- 
tion of  values  constantly  going  on  during  the  treatment  so 
that  while  the  solution  is  being  reduced  in  value  by  dilution 
it  is  constantly  being  augmented  by  the  solution  of  new  values, 
so  that  the  solution  finally  discharged  as  moisture  with  the 
slimes  tails  will  never  be  as  low  in  value  as  the  dilution  calls 
for.  Since  the  cost  of  applying  a dilution  of  definite  quantity  to 
the  slimes  is  the  same,  no  matter  what  the  value  extracted  by 
the  dilution  is,  it  will  be  seen  that  the  economic  limit  is  soon 
reached  where  further  dilution  will  not  pay.  Few  of  the  mills 
can  afford  to  apply  more  than  four  to  five  dilutions  profitably. 
It  must  also  be  borne  in  mind  that  with  an  increased  number 
of  dilutions  the  amount  of  solutions  to  be  handled  in  the  mill 
will  increase.  As  it  is,  at  present  the  mill  handles  a great  quan- 
tity of  solution  per  day.  The  application  of  an  extra  water  wash 
to  the  slimes  would,  however,  not  be  so  objectionable  if  the  de- 
cantations from  the  last  wash  were  run  to  waste  through  a large 
zinc  box  in  which  the  poorer  grade  of  shavings  and  the  dust  from 
the  lathe  could  be  utilized.  The  saving  made  in  this  way  would 
probably  be  appreciable. 

The  treatment  of  the  slimes  at  the  Hidden  Fortune  mill  is 
similar,  but  differs  in  details.  The  slimes  vats  are  first  filled 
with  barren  solution  and  the  slimes  pulp  is  charged  at  the  cen- 
ter of  the  vat  through  a large  pipe  which  leads  to  within  a few 
feet  of  the  bottom  of  the  vat.  The  clear  solution  overflows  con- 
tinually arcund  the  whole  of  the  periphery  being  collected  by 
an  annular  launder  and  taken  to  the  battery  sumps.  When  the 
outgoing  solution  becomes  cloudy  the  charging  of  the  slimes  is 
stopped  and  slimes  are  permitted  to  settle  the  clear  solution  at 


56 

the  top,  in  the  mean-time  being  decanted  to  the  battery  sump, 
in  a similar  way  described  for  the  Horseshoe  mill.  When  the 
solution  has  been  decanted  to  within  an  inch  or  two  of  the 
slimes  the  top  layer  of  thin  slimes,  to  a depth  of  three  or  four 
inches,  is  pumped  to  the  vat  that  is  tilling  with  slimes,  the  ob- 
ject oi  this  being  to  remove  as  much  solution  as  possible  in  or- 
der to  have  the  next  dilution  as  efficient  as  possible.  The  first 
wash  of  barren  solution  is  then  added,  this  being  added  through 
the  perforated  air  pipes  at  the  bottom  of  the  vat.  This  method 
of  adding  the  barren  solution  is  adopted,  first,  to  keep  the  per 
forations  of  the  air  pipes  clear,  and  second,  to  secure  the  agita- 
tion and  moving  of  the  heavier  slimes  at  the  bottom  of  the  vat 
After  the  addition  of  barren  solution  the  charge  of  slimes  is  ag- 
itated with  air  at  40  pounds  pressure  per  square  inch,  then  per- 
mitted to  settle  and  the  clear  solution  decanted  as  described. 

The  slimes  receive  three  washes  with  barren  solution  and 
one  with  water.  Before  the  slimes  are  finally  discharged  the 
top  layer,  to  a depth  of  three  or  four  inches,  is  again  pumped 
to  the  vat  which  is  filling.  The  tbtal  time  required  for  the 
treatment  of  the  slimes  is  between  three  and  four  days.  Three 
washes  are  found  sufficient  at  the  Hidden  Fortune  mill  since  the 
slimes  receive  an  unwatering  before  going  to  the  slimes  vats,  as 
has  been  described.  At  this  mill  the  extraction  made  on  slimes 
as  determined  by  the  assays  on  the  washed  tailings  is  80  percent. 
The  actual  recovery  is  but  7 5 per  cent,  as  determined  by  the 
unwashed  tailings,  showing  a loss  of  gold  of  five  per  cent  which 
goes  out  with  the  slimes  tailings  in  the  dissolved  form. 

The  second  method  of  treatment  in  which  the  slimes  are 
successively  transferred  from  one  vat  to  another  is  illustrated  by 
the  practice  at  the  Dakota  mill.  The  slimes  from  the  cones  are 
alternately  charged  into  the  loading  vats.  No’s.  1 and  2,  which  are 
20  feet  in  diameter  and  137  inches  deep.  Each  vat  is  filled  for 
twelve  hours  then  permitted  to  settle  for  ten  hours,  the  clear 
solution  at  the  top  being  continually  decanted  off,  finally  to 
within  one  inch  of  the  settled  slimes.  The  settled  slimes  are 
then  pumped  by  a centrifugal  pump  having  a four  inch  suction 
to  vat  No.  *3,  barren  solution  being  continually  added  to  the  suc- 
tion of  the  pump  during  the  transference  which  takes  from 
one  to  three  hours.  In  vat  No.  3 the  slimes  are  permitted  to 
settle  again  for  ten  hours,  the  clear  supernatent  solution  being 
decanted  off  meanwhile.  The  slimes  are  then  transferred  to  vat 
No.  4 by  the  pump,  barren  solution  being  added  to  the  suction. 
In  vat  No  4 the  slimes  receive  an  additional  agitation  by  pump- 


57 


mg  for  about  one  hour,  the  slimes  being  drawn  off  at  the  bottom 
of  the  vat  by  the  pump  and  returned  over  the  top.  The  settling 
and  decanting  is  then  repeated  and  the  slimes  transferred  to  vat 
No.  5,  From  this  vat  after  the  settling  and  the  decantation  of 
solution  the  slimes  are  transferred  to  vat  No.  6,  but  this  time 
with  wash  water  instead  of  barren  solution.  The  amount  of 
wash  water  added  is  equivalent  to  the  amount  of  moisture  in  the 
slimes.  In  vat  No.  6 the  last  settling  takes  place,  the  solution 
is  decanted  and  the  slimes  are  discharged.  Lime  for  the  coagu- 
lation of  the  slimes  is  added  to  the  extent  of  six  pounds  per  ton 
of  ore  at  the  batteries  The  time  required  for  the  treatment  of 
the  slimes  is  five  days. 

The  following  figures  on  slimes  treatment  at  the  Dakota 
mill  are  of  considerable  interest:  In  5.5  months  6,681.67  tons  of 
slimes  were  treated,  the  slimes  amounting  to  33  per  cent  of  the 
ores  crushed.  The  average  value  of  ore  during  this  period  was 
$4  75  per  ton.  The  slimes  tailings  dried  and  unwashed  assayed 
Si. 3 1 per  ton,  giving  a recovery  on  the  slimes  of  72. 28  per  cent. 
The  washed  slimes  tailings  assayed  $0,912,  showing  a solution  of 
the  values  of  80.7  per  cent  and  a loss  of  soluble  gold  of  40  cents 
per  ton  or  8.42  per  cent  of  the  value  of  the  ore.  The  slimes  are 
discharged  with  50  per  cent  moisture,  this  moisture  consisting  of 
solution  having  a strength  of  1.07  pounds  of  cyanide  per  ton. 
Since  there  is  a ton  of  this  solution  going  to  waste  for  every  ton 
of  dry  slimes  discharged,  in  the  5.5  months  which  the  above  pe- 
riod covers,  there  were  lost  7, 147.  6 pounds  of  cyanide  which,  at 
23  cents  per  pound  had  a value  of  $1/644.  Adding  to  this  the 
loss  in  dissolved  gold  amounting  to  $2,672,  the  total  loss  is 
*>4,316,  or  64  cents  per  ton. 

These  figures  show  clearly  the  weak  points  of  the  decanta- 
tion system  of  slimes  treatment.  The  Dakota  Mill  is  one  of  the 
most  successful  mills  in  the  district,  treating  what  is  practically 
the  lowest  grade  of  siliceous  ores  handled  in  the  district.  The 
results  on  sands  at  this  mill  are  discussed  under  sand  treatment. 
The  treatment  of  the  slimes  at  the  Maitland  Mill  is  similar  to 
that  at  the  Dakota.  Each  ton  of  dry  slimes  receives  a treatment 
by  5.38  tons  of  barren  solution  and  0.96  tons  of  wash  water.  The 
solution  going  out  with  the  slimes  as  moisture  contain  $0.46  in 
gold  per  ton.  The  head  slimes  solution  or  the  solution  first  de- 
canted from  the  slimes  while  filling  has  a value  of  about  $2  co 
per  ton. 


58 

At  the  Lundborg,  Dorr  & Wilson  mill  the  Moore  slimes 
process  is  used  on  the  slimes.  There  are  three  rectangular  vats  15 
feet  long,  7 feet  wide  and  5. 5 feet  deep.  The  first  tank  has  a 
double  hopoer  bottom,  the  sides  inclined  at  45  degrees  to 
more  readily  collect  the  heavy  slimes  which  sometimes  fail  to 
be  taken  on  the  filter  frames.  There  is  a set  of  35  frames  4.5 
by  6 feet  in  area  and  made  of  two  inch  material.  The 
filtering  medium  is  18  ounce  duck.  Both  sides  of  the  frames 
are  effective  as  filters  and  the  total  filtering  area  is  1836 
square  feet.  The  interior  of  the  frames  are  connected  with  a 
pump  which  produces  suction  and  also  with  a compressor. 
The  suction  is  equivalent  to  18  inches  of  mercury.  The  set  of 
frames  is  suspended  from  a hydraulic  crane  which  transfers  the 
frames  from  one  vat  to  the  other.  The  method  of  treatment  is  as 
follows:  The  slimes  after  agitation  by  air  and  a centrifugal  pump 
in  an  eight  foot  sheet  iron  cone  are  run  to  the  first  tank  of  the 
Moore  process,  the  frames  are  immersed  in  the  slimes  and  the 
suction  is  started.  A coating  of  slimes  deposits  on  the  filters  and 
the  clear  solutionis  discharged  by  the  pump.  When  the  slimes 
layer  on  the  filters  has  accumulated  to  the  thickness  of  an  inch, 
which  amounts  to  a load  of  four  tons  on  the  set  of  frames,  and  takes 
from  40  to  65  minutes,  the  frames  are  lifted  out  with  their  ad- 
herent load  of  slimes,  suction  meanwhile  being  continued,  and 
immersed  in  the  next  vat  which  is  filled  with  barren  solution.  This 
barren  solution  is  sucked  through  the  slimes  for  40  minutes,  when 
the  frames  are  transferred  to  the  next  vat  which  is  filled  with 
water.  This  water  is  sucked  through  the  slimes  for  40  minutes, 
when  the  frames  are  lifted  out,  transferred  to  above  the  discharge 
hopper,  the  suction  changed  to  pressure,  which  causes  the  slimes 
to  peel  off  into  cars  below  the  hopper.  Some  little  scraping  has 
to  be  done  to  clean  the  frames.  No  figures  are  as  yet  available 
concerning  the  results  of  the  Moore  process,  permitting  of  a 
comparison  with  the  decantation  process.  It  is  a fact  however 
that  the  process  discharges  dryer  slimes,  those  at  the  Lundborg, 
Dorr  & Wilson  mill  containing  from  34  to  36  percent  moisture, 
aslagainst  50  percent,  which  is  the  usual  figure  for  the  decantation 
process.  At  the  mills  where  the  upper  layer  oj  slimes  is  pumped 
off  as  described  for  the  Hidden  Fortune  mill  the  slimes  are  dis- 
charged with  46  to  47  per  cent  moisture.  Some  of  the  mills  of 
the  district  which  must  confine  their  tailings  within  narrow  limits 
and  cannot  let  them  flow  freely  to  waste,  experience  consider- 
able trouble  from  the  high  moisture  contents  of  their  slimes  tail- 


Filter  Frames,  Moore  Slimes  Process. 


59 

mgs.  The  slimes  tailings  from  the  Moore  process  are  much 
more  easily  held  in  check.  In  making  a general  comparison  be- 
tween the  Moore  and  the  decantation  process  it  must  be  borne 
in  mind  that  the  slimes  are  under  trea  merit  in  the  Moore  pro- 
cess only  two  to  three  hours,  and  in  that  time  receive  practi- 
cally no  agitation,  so  that  the  solution  of  the  gold  must  take  place 
practically  before  the  slimes  go  to  the  Moore  process.  The 
Moore  process,  even  with  separate  agitation  however  shortens 
the  time  on  the  slimes  materially  and  a large  capacity  can  be  in 
stalled  within  a small  space. 

Filter  press  experiments  have  been  made  on  a fair  sized 
scale  at  one  of  the  mills  in  the  district,  which  indicated  that 
slimes  could  be  made|containing  about  25  per  cent  moisture  and 
that  these  slimes,  on  account  of  the  close  washing  feasible,  car- 
ried very  little  cyanide  and  dissolved  gold.  It  would  not  be 
surprising  to  eventually  see  filter  pressing  replace  the  de- 
cantation process  at  least  in  part. 

THE  DISTRIBUTION  OF  SOLUTIONS  IN  THE 
MILLS. — The  distribution  of  solutions  in  the  mills  is  quite  com- 
plex. and  the  following  diagrams  show  the  general  practice. 
Distribution  of  solutions  at  the  Horseshoe  mill. 

Battery  Solution  Storage 
Batteries 


Cones 

/ 


Slimes 


Slimes  Vats 


/ 

/ . 

decanted  solution 
returned  to  bat- 
tery solution  stor- 
age. 


\ 

\ 

overflow 
while  filling 
standardized 
.and  then  to 
sand  vats. 


Sands 

I 

Sand  Vats 

1 


Solution 
to  pre- 
cipitating 
barrels. 

7 


Wash  water  goes 
to  battery  solut- 
ion storage. 


/ 


/ 


Barren  Solution 

goes,  to  slime  vats,  sand  vats  and 
battery  solution  storage. 

It  will  be  noticed  that  the  only  solution  going  to  the  precip- 
itating boxes  is  that  which  has  passed  the  sands.  This  amounts 


6o 


to  from  Soo  to  1,000  toas  per  day.  The  battery  solution  has  a 
gold  value  of  approximately  one  dollar  per  ton.  This 
value  is  derived  for  the  greater  part  from  the  decanted  slimes 
solution.  The  cyanide  needed  to  bring  up  the  strength  of  the 
solution  is  added  to  a comparatively  small  amount  of  decanted 
slimes  solution,  more  particularly  the  overflow  solution  from  the 
slimes  vats  while  these  are  filling.  This  is  brought  up  to  three 
to  four  pounds  of  cyanide  per  ton  and  run  qji  the  sands  so  that 
these  get  the  benefit  of  what  is  practically  a strong  solution. 

In  the  scheme  of  the  Maitland  mill  which  follows,  it  will 
again  be  noticed  that  the  only  solution  that  is  precipitated  is 
that  which  has  passed  the  sands.  This  is  the  general  practice 
at  all  of  the  mills.  The  solution  is  restandardized  ahead  of  the 
zinc  boxes  in  order  to  get  more  efficient  precipitation  as  there  is 
some  copper  in  the  solution.  The  strength  of  the  various  solu- 
tions at  the  different  mills  is  given  under  the  discussion  of  the 
treatment  of  the  sands.  The  battery  solution  in  the  case  of  the 
Maitland  mill  has  a value  of  about  50  cents  of  gold  per  ton  and 
the  barren  solution  about  ten  cents  per  ton.  About  1,100  tons 
of  battery  solution  are  pumped  per  day  and  close  to  500  tons  of 
solution  are  precipitated  every  day,  which,  after  precipitation, 
becomes  the  barren  solution,  so  that  the  mill  handles  per  day 
about  1,600  tons  of  solution,  which,  with  a capacity  of  120  tons 
of  ore  per  day,  is  13. 1 tons  of  solution  per  ton  of  ore.  The 
pumping  expense  of  a wet  crushing  mill  per  day  is  appreciable 
and  in  the  design  of  a mill  the  question  of  handling  the  solu- 
tions is  a very  important  one.  At  one  of  the  mills  the  restand- 
ardization takes  place  in  the  battery  sump  so  that  the  strongest 
solution  is  used  in  the  battery.  This  practice  is  for  obvious  rea- 
sons not  the  best. 


Distribution  of  Solutions  at  the  Maitland  Mill . 

Battery  Solution  Storage. 


Slimes  Vats  Sand  Vats 

/ i 

decanted  solution  and  overflow  gold  solution 

while  filling  from  sump  to  bat- 
tery solution  storage.  gold  tank  (standarized  in 

| this  tank.) 

Precipitating  Boxes 

I 

Barren  Solution 
375  tons  to  Slimes  Vats  and  125 
tons  to  Sand  Vats. 

THE  PRECIPITATION  OF  THE  VALUES  - In  gen- 
eral no  troubles  in  precipitation  are  encountered  in  the  form 
the  process  is  employed  at  the  present  time.  In  the  earlier  prac" 
tice  of  the  mills  when  decanted  slimes  solution  was  passed 
through  the  zinc  boxes  with  the  idea  of  keeping  the  battery  solution 
practically  free  from  gold  values  trouble  was  experienced  by 
getting  a very  bulky  and  low  grade  precipitate  on  account  of 
the  accumulation  of  fine  ore  slimes  in  the  boxes,  but  in  the  pres- 
ent practice  this  trouble  is  avoided  as  described.  At  the  Da- 
kota and  Horseshoe  mills  precipitation  is  carried  on  in  barrels. 
These  at  the  Horseshoe  mill  are  two  feet  in  diameter  and  two 
feet  high,  holding  five  cubic  feet  of  zinc,  or  25  pounds.  120  of 
those  barrels  are  in  use.  The  barrels  can  readily  be  taken  up  on 


62 


a pulley  gear  running  on  a trolley  and  conveyed  to  the  clean-up 
tank  for  discharge  and  cleaning.  At  the  Horseshoe  mill  where 
225  to  250  tons  of  ore  are  treated  per  day,  1,000  tons  of  solu- 
tion are  precipitated  every  24  hours.  The  zinc  consumption 
is  one  pound  per  ton  of  ore  treated.  At  the  Dakota  Mill  it  is 
0.58  pounds  At  the  Hidden  Fortune  and  the  Maitland  mills 
precipitation  is  carried  on  in  the  usual  form  of  iron  zinc  boxes. 
At  the  Maitland  Mill  treating  120  tons  per  day  there  are  four 
boxes  of  eight  compartments  each,  the  compartment  having  a 
capacity  of  seven  cubic  feet  of  zinc.  From  450  to  500  tons  of 
solution  are  precipitated  per  day,  there  being  2.13  tons  of  solu- 
tion for  each  cubic  foot  of  zinc.  The  solution  entering  the  boxes 
is  kept  at  2.5  pounds  of  cyanide  per  ton,  fora  lower  tenor  causes 
trouble  by  copper  precipitating,  which  the  solutions  carry  to  a 
small  extent.  The  zinc  consumption  is  0.  3 of  a pound  per  ton 
of  solution  precipitated  and  1.33  pounds  per  ton  of  ore  treated. 

TREA  TMENTOF  THE  PRECIPITA  TES  — The  precip- 
itates are  refined  at  all  of  the  mills  by  the  usual  sulphuric  acid 
method  into  bullion  which  is  disposed  of  to  the  United  States 
Assay  Office  at  Deadwood  The  fineness  of  bullion  varies  at 
the  different  mills  as  .the  silver  contents  of  the  ores  vary  con- 
siderably. However,  at  most  of  the  mills  the  bullion  pro- 
duced ranges  between  450  and  600  fine  in  gold.  In  order  to  dis- 
pose of  the  bullion  to  the  Government  Assay  Office  at  Deadwood, 
the  bullion  must  have  a minimum  fineness  of  600  in  gold  and 
at  some  ofjthe  mills  in  the  smelting  of  the  precipitates  a matte  is 
purposely  formed  so  that  the  resultiug  bullion  will  be  above  the 
minimum  limit.  The  slags  from  the  smelting  of  the  precipitates 
are  disposed  of  to  the  smelters  at  Denver,  although  at  the 
Horseshoe  Mill  the  slags  and  matte  from  the  smeltings  are  re- 
fined by  melting  with  litharge  and  cupelling  the  resultant 
bullion. 

GENERAL  EXTRACTION  FIGURES.— The  extraction 
at  the  mills  varies  from  68  to  75  per  cent,  according  to  the  ores 
treated.  At  the  Maitland  Mill  where  the  extraction  is  73.2  per 
cent  and  where  approximately  half  the  ore  is  treated  as  slimes 
and  half  as  sauds  the  extraction  is  distributed  as  follows,  39  per 
cent  is  extracted  in  the  batteries  and  cones,  16.5  per  cent  in  the 
slime  treatment,  and  17  oer  cent  in^  the  sand  treatment.  As  a 
general  thing  the  recovery  of  bullion  is  either  two  to  three  per 
cent  higher  or  the  same  amount  lower  than  the  assays  of  the 
ores,  tailings  and  solutions  call  for. 


Precipitating  Floor,  Mogul  Mill,  Horseshoe  Mining  Company 


63 

THE  COST  OF  TREATMENT. 

The  following  is  the  detailed  cost  of  treatment  at  the  Da- 
kota Mill  during  a period  in  1902.  The  average  value  of  the  ore 


was  $4.70  per  ton. 

Labor 45-3° 

Superintendence 9.0 

Cyanide ai.i 

Zinc 3*3 

Lime 1.2 

Power  22  6 

Shoes,  dies,  etc 9.5 

Repairs 2.7 

Refining 3. 

Assay  Office  4. 

General  Expense 50 


Total .127.7  $i.27per  ton. 

The  mill  during  this  period  treatod  100  tons  per  day.  The 
cost  at  the  Dakota  Mill,  at  the  present  time  owing  to  a somewhat 
increased  capacity  has  been  reduced  to  $1.17  per  ton. 

The  cost  at  the  Maitland  Mill  treating  about  125  per  ton  per 
day,  and  which  is  not  situated  on  the  railro  ad  so  that  the  cost  of 
supplies  is  considerably  increased,  is  $1.79  per  ton.  The  cost  at 
the  other  mills  ranges  between  the  costs  at  the  two  mills 
given. 


Note.  This  paper  is  printed  in  advance,  by  permission, 
from  the  T.  A.  I.  M.  E. , September  1904. 

Note.  The  author  wishes  to  acknowledge  his  indebtedness 
for  much  information  contained  in  the  above  paper  to  Mr.  John 
Gross  of  the  Maitland  Mill,  to  Mr.  John  Ingersol  of  the  Dakota 
Mill,  Mr.  J.  V.  N.  Dorr,  of  the  Lundborg,  Dorr  & Wilson  Mill, 
to  Mr.  Freeman  Steele  of  the  Hidden  Fortune  Mill  and  to  Mr. 
G.  H.  Clevenger  of  the  Horseshoe  Mill. 


